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	$205.82	13.756%	$234.1326	$234.13	$234.15	$234.10
Purchase #2	$181.51	10.557%	$200.672	$200.67	$200.65	$200.70
Purchase #3	$7.81	3.530%	$8.0857	$8.09	$8.10	$8.10
Purchase #4	$187.42	12.812%	$211.4323	$211.43	$211.45	$211.40
Purchase #5	$124.25	10.709%	$137.5559	$137.56	$137.55	$137.60
Purchase #6	$72.74	3.240%	$75.0968	$75.10	$75.10	$75.10
Purchase #7	$78.72	13.795%	$89.5794	$89.58	$89.60	$89.60
7 purchase totals =	$858.27		$956.5547	$956.56	$956.60	$956.60