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	$231.79	10.391%	$255.8753	$255.88	$255.90	$255.90
Purchase #2	$130.50	6.799%	$139.3727	$139.37	$139.35	$139.40
Purchase #3	$173.83	11.384%	$193.6188	$193.62	$193.60	$193.60
Purchase #4	$149.88	10.616%	$165.7913	$165.79	$165.80	$165.80
Purchase #5	$198.47	12.733%	$223.7412	$223.74	$223.75	$223.70
Purchase #6	$58.48	12.173%	$65.5988	$65.60	$65.60	$65.60
Purchase #7	$77.87	13.293%	$88.2213	$88.22	$88.20	$88.20
7 purchase totals =	$1,020.82		$1,132.2194	$1,132.22	$1,132.20	$1,132.20