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	$53.57	10.806%	$59.3588	$59.36	$59.35	$59.40
Purchase #2	$153.73	7.758%	$165.6564	$165.66	$165.65	$165.70
Purchase #3	$28.27	13.702%	$32.1436	$32.14	$32.15	$32.10
Purchase #4	$103.79	7.420%	$111.4912	$111.49	$111.50	$111.50
Purchase #5	$111.53	9.238%	$121.8331	$121.83	$121.85	$121.80
Purchase #6	$84.32	5.323%	$88.8084	$88.81	$88.80	$88.80
Purchase #7	$88.88	12.706%	$100.1731	$100.17	$100.15	$100.20
7 purchase totals =	$624.09		$679.4646	$679.46	$679.45	$679.50