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	$142.65	12.493%	$160.4713	$160.47	$160.45	$160.50
Purchase #2	$94.60	10.452%	$104.4876	$104.49	$104.50	$104.50
Purchase #3	$122.38	11.558%	$136.5247	$136.52	$136.50	$136.50
Purchase #4	$196.87	13.708%	$223.8569	$223.86	$223.85	$223.90
Purchase #5	$207.78	10.168%	$228.9071	$228.91	$228.90	$228.90
Purchase #6	$61.31	8.240%	$66.3619	$66.36	$66.35	$66.40
Purchase #7	$130.45	3.105%	$134.5005	$134.50	$134.50	$134.50
7 purchase totals =	$956.04		$1,055.1100	$1,055.11	$1,055.05	$1,055.20