Basic petty cash solution - Imprest

[AndyCan]

I need to add a basic petty cash module to my current database and would like some advice on how to set it up from others who have more experience in the matter.

I'm thinking of just a basic table with ID, Description, Category, Credit and Debit fields and use it as a type of never-ending list. However I'm not sure how I would manage the running total or indeed whether I should have a parent table for each petty cash cycle (time between replenishments) and use the previously mentioned table as Petty Cash Line Items.

Has anyone done this before? I'm sure it's quite simple... I just need a shove in the right direction.

Thanks!