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	$60.37	10.741%	$66.8543	$66.85	$66.85	$66.90
Purchase #2	$159.85	12.645%	$180.063	$180.06	$180.05	$180.10
Purchase #3	$136.83	12.186%	$153.5041	$153.50	$153.50	$153.50
Purchase #4	$105.37	6.137%	$111.8366	$111.84	$111.85	$111.80
Purchase #5	$115.25	11.729%	$128.7677	$128.77	$128.75	$128.80
Purchase #6	$5.43	8.211%	$5.8759	$5.88	$5.90	$5.90
Purchase #7	$241.29	9.733%	$264.7748	$264.77	$264.75	$264.80
7 purchase totals =	$824.39		$911.6764	$911.67	$911.65	$911.80