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	$200.61	10.298%	$221.2688	$221.27	$221.25	$221.30
Purchase #2	$244.72	13.555%	$277.8918	$277.89	$277.90	$277.90
Purchase #3	$37.30	5.369%	$39.3026	$39.30	$39.30	$39.30
Purchase #4	$70.53	9.410%	$77.1669	$77.17	$77.15	$77.20
Purchase #5	$7.99	6.197%	$8.4851	$8.49	$8.50	$8.50
Purchase #6	$150.89	3.283%	$155.8437	$155.84	$155.85	$155.80
Purchase #7	$242.72	4.863%	$254.5235	$254.52	$254.50	$254.50
7 purchase totals =	$954.76		$1,034.4824	$1,034.48	$1,034.45	$1,034.50