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	$38.60	9.210%	$42.1551	$42.16	$42.15	$42.20
Purchase #2	$26.56	6.724%	$28.3459	$28.35	$28.35	$28.30
Purchase #3	$98.36	5.195%	$103.4698	$103.47	$103.45	$103.50
Purchase #4	$37.67	7.527%	$40.5054	$40.51	$40.50	$40.50
Purchase #5	$127.67	6.634%	$136.1396	$136.14	$136.15	$136.10
Purchase #6	$157.68	8.218%	$170.6381	$170.64	$170.65	$170.60
Purchase #7	$160.77	9.430%	$175.9306	$175.93	$175.95	$175.90
7 purchase totals =	$647.31		$697.1845	$697.20	$697.20	$697.10