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	$40.80	10.650%	$45.1452	$45.15	$45.15	$45.10
Purchase #2	$69.29	12.767%	$78.1363	$78.14	$78.15	$78.10
Purchase #3	$138.90	5.751%	$146.8881	$146.89	$146.90	$146.90
Purchase #4	$138.39	3.592%	$143.361	$143.36	$143.35	$143.40
Purchase #5	$42.81	12.548%	$48.1818	$48.18	$48.20	$48.20
Purchase #6	$32.57	10.745%	$36.0696	$36.07	$36.05	$36.10
Purchase #7	$28.38	11.388%	$31.6119	$31.61	$31.60	$31.60
7 purchase totals =	$491.14		$529.3939	$529.40	$529.40	$529.40