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	$75.25	13.594%	$85.4795	$85.48	$85.50	$85.50
Purchase #2	$159.29	7.453%	$171.1619	$171.16	$171.15	$171.20
Purchase #3	$157.84	7.570%	$169.7885	$169.79	$169.80	$169.80
Purchase #4	$69.30	12.845%	$78.2016	$78.20	$78.20	$78.20
Purchase #5	$46.60	11.823%	$52.1095	$52.11	$52.10	$52.10
Purchase #6	$58.58	13.646%	$66.5738	$66.57	$66.55	$66.60
Purchase #7	$48.73	7.162%	$52.22	$52.22	$52.20	$52.20
7 purchase totals =	$615.59		$675.5348	$675.53	$675.50	$675.60