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	$146.35	12.439%	$164.5545	$164.55	$164.55	$164.60
Purchase #2	$222.52	12.617%	$250.5953	$250.60	$250.60	$250.60
Purchase #3	$178.33	12.240%	$200.1576	$200.16	$200.15	$200.20
Purchase #4	$118.45	8.236%	$128.2055	$128.21	$128.20	$128.20
Purchase #5	$137.37	6.660%	$146.5188	$146.52	$146.50	$146.50
Purchase #6	$57.52	4.181%	$59.9249	$59.92	$59.90	$59.90
Purchase #7	$40.92	10.337%	$45.1499	$45.15	$45.15	$45.10
7 purchase totals =	$901.46		$995.1065	$995.11	$995.05	$995.10