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	$66.83	5.494%	$70.5016	$70.50	$70.50	$70.50
Purchase #2	$30.83	13.360%	$34.9489	$34.95	$34.95	$34.90
Purchase #3	$217.89	7.198%	$233.5737	$233.57	$233.55	$233.60
Purchase #4	$197.41	12.562%	$222.2086	$222.21	$222.20	$222.20
Purchase #5	$165.75	7.741%	$178.5807	$178.58	$178.60	$178.60
Purchase #6	$149.30	8.293%	$161.6814	$161.68	$161.70	$161.70
Purchase #7	$86.73	4.714%	$90.8185	$90.82	$90.80	$90.80
7 purchase totals =	$914.74		$992.3134	$992.31	$992.30	$992.30