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	$120.33	3.550%	$124.6017	$124.60	$124.60	$124.60
Purchase #2	$49.27	12.693%	$55.5238	$55.52	$55.50	$55.50
Purchase #3	$172.91	11.418%	$192.6529	$192.65	$192.65	$192.70
Purchase #4	$21.68	13.785%	$24.6686	$24.67	$24.65	$24.70
Purchase #5	$112.82	4.314%	$117.6871	$117.69	$117.70	$117.70
Purchase #6	$84.90	12.169%	$95.2315	$95.23	$95.25	$95.20
Purchase #7	$52.82	3.861%	$54.8594	$54.86	$54.85	$54.90
7 purchase totals =	$614.73		$665.2250	$665.22	$665.20	$665.30