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	$243.79	3.638%	$252.6591	$252.66	$252.65	$252.70
Purchase #2	$75.71	8.539%	$82.1749	$82.17	$82.15	$82.20
Purchase #3	$241.58	12.802%	$272.5071	$272.51	$272.50	$272.50
Purchase #4	$119.27	13.700%	$135.61	$135.61	$135.60	$135.60
Purchase #5	$55.88	6.191%	$59.3395	$59.34	$59.35	$59.30
Purchase #6	$66.45	8.314%	$71.9747	$71.97	$71.95	$72.00
Purchase #7	$65.59	11.822%	$73.344	$73.34	$73.35	$73.30
7 purchase totals =	$868.27		$947.6093	$947.60	$947.55	$947.60