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	$144.77	13.387%	$164.1504	$164.15	$164.15	$164.20
Purchase #2	$105.41	5.638%	$111.353	$111.35	$111.35	$111.40
Purchase #3	$179.66	11.637%	$200.567	$200.57	$200.55	$200.60
Purchase #4	$116.75	11.334%	$129.9824	$129.98	$130.00	$130.00
Purchase #5	$83.48	9.427%	$91.3497	$91.35	$91.35	$91.30
Purchase #6	$93.95	6.850%	$100.3856	$100.39	$100.40	$100.40
Purchase #7	$149.95	5.825%	$158.6846	$158.68	$158.70	$158.70
7 purchase totals =	$873.97		$956.4727	$956.47	$956.50	$956.60