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	$150.84	9.730%	$165.5167	$165.52	$165.50	$165.50
Purchase #2	$156.37	11.575%	$174.4698	$174.47	$174.45	$174.50
Purchase #3	$170.26	8.606%	$184.9126	$184.91	$184.90	$184.90
Purchase #4	$118.54	9.247%	$129.5014	$129.50	$129.50	$129.50
Purchase #5	$42.78	3.733%	$44.377	$44.38	$44.40	$44.40
Purchase #6	$199.41	12.230%	$223.7978	$223.80	$223.80	$223.80
Purchase #7	$66.32	8.107%	$71.6966	$71.70	$71.70	$71.70
7 purchase totals =	$904.52		$994.2719	$994.28	$994.25	$994.30