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	$150.74	11.634%	$168.2771	$168.28	$168.30	$168.30
Purchase #2	$157.64	4.640%	$164.9545	$164.95	$164.95	$165.00
Purchase #3	$206.41	13.714%	$234.7171	$234.72	$234.70	$234.70
Purchase #4	$94.81	10.541%	$104.8039	$104.80	$104.80	$104.80
Purchase #5	$218.69	11.743%	$244.3708	$244.37	$244.35	$244.40
Purchase #6	$161.61	5.749%	$170.901	$170.90	$170.90	$170.90
Purchase #7	$104.69	3.733%	$108.5981	$108.60	$108.60	$108.60
7 purchase totals =	$1,094.59		$1,196.6225	$1,196.62	$1,196.60	$1,196.70