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	$228.96	13.756%	$260.4557	$260.46	$260.45	$260.50
Purchase #2	$41.76	9.594%	$45.7665	$45.77	$45.75	$45.80
Purchase #3	$82.90	13.702%	$94.259	$94.26	$94.25	$94.30
Purchase #4	$22.29	11.512%	$24.856	$24.86	$24.85	$24.90
Purchase #5	$105.27	5.636%	$111.203	$111.20	$111.20	$111.20
Purchase #6	$205.80	12.303%	$231.1196	$231.12	$231.10	$231.10
Purchase #7	$205.84	9.543%	$225.4833	$225.48	$225.50	$225.50
7 purchase totals =	$892.82		$993.1431	$993.15	$993.10	$993.30