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	$50.58	11.299%	$56.295	$56.30	$56.30	$56.30
Purchase #2	$82.37	7.842%	$88.8295	$88.83	$88.85	$88.80
Purchase #3	$149.76	6.816%	$159.9676	$159.97	$159.95	$160.00
Purchase #4	$34.53	7.753%	$37.2071	$37.21	$37.20	$37.20
Purchase #5	$80.59	12.148%	$90.3801	$90.38	$90.40	$90.40
Purchase #6	$166.57	4.160%	$173.4993	$173.50	$173.50	$173.50
Purchase #7	$8.31	10.733%	$9.2019	$9.20	$9.20	$9.20
7 purchase totals =	$572.71		$615.3805	$615.39	$615.40	$615.40