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	$106.52	4.685%	$111.5105	$111.51	$111.50	$111.50
Purchase #2	$28.90	11.715%	$32.2856	$32.29	$32.30	$32.30
Purchase #3	$177.31	8.198%	$191.8459	$191.85	$191.85	$191.80
Purchase #4	$131.93	12.135%	$147.9397	$147.94	$147.95	$147.90
Purchase #5	$90.89	3.130%	$93.7349	$93.73	$93.75	$93.70
Purchase #6	$143.93	12.143%	$161.4074	$161.41	$161.40	$161.40
Purchase #7	$64.54	10.360%	$71.2263	$71.23	$71.25	$71.20
7 purchase totals =	$744.02		$809.9503	$809.96	$810.00	$809.80