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	$37.37	11.374%	$41.6205	$41.62	$41.60	$41.60
Purchase #2	$97.98	13.717%	$111.4199	$111.42	$111.40	$111.40
Purchase #3	$43.50	11.448%	$48.4799	$48.48	$48.50	$48.50
Purchase #4	$152.49	3.494%	$157.818	$157.82	$157.80	$157.80
Purchase #5	$108.70	4.139%	$113.1991	$113.20	$113.20	$113.20
Purchase #6	$28.62	13.191%	$32.3953	$32.40	$32.40	$32.40
Purchase #7	$92.57	9.687%	$101.5373	$101.54	$101.55	$101.50
7 purchase totals =	$561.23		$606.4700	$606.48	$606.45	$606.40