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	$215.91	12.314%	$242.4972	$242.50	$242.50	$242.50
Purchase #2	$123.27	11.245%	$137.1317	$137.13	$137.15	$137.10
Purchase #3	$111.51	6.350%	$118.5909	$118.59	$118.60	$118.60
Purchase #4	$65.59	8.224%	$70.9841	$70.98	$71.00	$71.00
Purchase #5	$242.29	4.365%	$252.866	$252.87	$252.85	$252.90
Purchase #6	$6.56	12.389%	$7.3727	$7.37	$7.35	$7.40
Purchase #7	$141.81	3.430%	$146.6741	$146.67	$146.65	$146.70
7 purchase totals =	$906.94		$976.1167	$976.11	$976.10	$976.20