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	$135.51	11.501%	$151.095	$151.10	$151.10	$151.10
Purchase #2	$20.70	8.554%	$22.4707	$22.47	$22.45	$22.50
Purchase #3	$40.50	5.640%	$42.7842	$42.78	$42.80	$42.80
Purchase #4	$10.35	11.281%	$11.5176	$11.52	$11.50	$11.50
Purchase #5	$43.88	3.788%	$45.5422	$45.54	$45.55	$45.50
Purchase #6	$225.38	6.594%	$240.2416	$240.24	$240.25	$240.20
Purchase #7	$34.67	13.644%	$39.4004	$39.40	$39.40	$39.40
7 purchase totals =	$510.99		$553.0517	$553.05	$553.05	$553.00