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	$151.36	9.797%	$166.1887	$166.19	$166.20	$166.20
Purchase #2	$59.27	12.137%	$66.4636	$66.46	$66.45	$66.50
Purchase #3	$144.38	6.561%	$153.8528	$153.85	$153.85	$153.90
Purchase #4	$113.86	3.317%	$117.6367	$117.64	$117.65	$117.60
Purchase #5	$171.37	5.310%	$180.4697	$180.47	$180.45	$180.50
Purchase #6	$36.45	7.361%	$39.1331	$39.13	$39.15	$39.10
Purchase #7	$221.76	3.330%	$229.1446	$229.14	$229.15	$229.10
7 purchase totals =	$898.45		$952.8892	$952.88	$952.90	$952.90