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	$65.59	7.614%	$70.584	$70.58	$70.60	$70.60
Purchase #2	$25.38	11.550%	$28.3114	$28.31	$28.30	$28.30
Purchase #3	$41.78	4.191%	$43.531	$43.53	$43.55	$43.50
Purchase #4	$160.54	3.733%	$166.533	$166.53	$166.55	$166.50
Purchase #5	$206.96	10.567%	$228.8295	$228.83	$228.85	$228.80
Purchase #6	$114.58	10.410%	$126.5078	$126.51	$126.50	$126.50
Purchase #7	$146.71	8.472%	$159.1393	$159.14	$159.15	$159.10
7 purchase totals =	$761.54		$823.4360	$823.43	$823.50	$823.30