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	$228.70	12.224%	$256.6563	$256.66	$256.65	$256.70
Purchase #2	$232.72	4.479%	$243.1435	$243.14	$243.15	$243.10
Purchase #3	$117.60	9.461%	$128.7261	$128.73	$128.75	$128.70
Purchase #4	$140.72	8.457%	$152.6207	$152.62	$152.60	$152.60
Purchase #5	$69.34	10.235%	$76.4369	$76.44	$76.45	$76.40
Purchase #6	$192.34	4.251%	$200.5164	$200.52	$200.50	$200.50
Purchase #7	$37.31	12.285%	$41.8935	$41.89	$41.90	$41.90
7 purchase totals =	$1,018.73		$1,099.9934	$1,100.00	$1,100.00	$1,099.90