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	$46.64	13.142%	$52.7694	$52.77	$52.75	$52.80
Purchase #2	$164.93	4.689%	$172.6636	$172.66	$172.65	$172.70
Purchase #3	$124.90	12.804%	$140.8922	$140.89	$140.90	$140.90
Purchase #4	$144.89	4.729%	$151.7418	$151.74	$151.75	$151.70
Purchase #5	$172.57	3.857%	$179.226	$179.23	$179.25	$179.20
Purchase #6	$21.37	6.292%	$22.7146	$22.71	$22.70	$22.70
Purchase #7	$226.43	10.521%	$250.2527	$250.25	$250.25	$250.30
7 purchase totals =	$901.73		$970.2603	$970.25	$970.25	$970.30