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	$77.44	3.111%	$79.8492	$79.85	$79.85	$79.80
Purchase #2	$92.51	7.658%	$99.5944	$99.59	$99.60	$99.60
Purchase #3	$106.91	11.806%	$119.5318	$119.53	$119.55	$119.50
Purchase #4	$40.86	11.384%	$45.5115	$45.51	$45.50	$45.50
Purchase #5	$119.26	6.864%	$127.446	$127.45	$127.45	$127.40
Purchase #6	$108.81	6.759%	$116.1645	$116.16	$116.15	$116.20
Purchase #7	$78.70	7.311%	$84.4538	$84.45	$84.45	$84.50
7 purchase totals =	$624.49		$672.5512	$672.54	$672.55	$672.50