Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$82.93	9.629%	$90.9153	$90.92	$90.90	$90.90
Purchase #2	$99.52	11.657%	$111.121	$111.12	$111.10	$111.10
Purchase #3	$212.88	8.628%	$231.2473	$231.25	$231.25	$231.20
Purchase #4	$173.25	5.562%	$182.8862	$182.89	$182.90	$182.90
Purchase #5	$247.55	3.630%	$256.5361	$256.54	$256.55	$256.50
Purchase #6	$230.69	3.717%	$239.2647	$239.26	$239.25	$239.30
Purchase #7	$180.51	8.596%	$196.0266	$196.03	$196.05	$196.00
7 purchase totals =	$1,227.33		$1,307.9972	$1,308.01	$1,308.00	$1,307.90