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	$216.66	3.213%	$223.6213	$223.62	$223.60	$223.60
Purchase #2	$146.65	8.597%	$159.2575	$159.26	$159.25	$159.30
Purchase #3	$88.87	12.217%	$99.7272	$99.73	$99.75	$99.70
Purchase #4	$36.64	11.570%	$40.8792	$40.88	$40.90	$40.90
Purchase #5	$172.29	12.721%	$194.207	$194.21	$194.20	$194.20
Purchase #6	$141.47	4.793%	$148.2507	$148.25	$148.25	$148.30
Purchase #7	$69.98	12.532%	$78.7499	$78.75	$78.75	$78.70
7 purchase totals =	$872.56		$944.6928	$944.70	$944.70	$944.70