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	$153.76	4.639%	$160.8929	$160.89	$160.90	$160.90
Purchase #2	$140.75	3.851%	$146.1703	$146.17	$146.15	$146.20
Purchase #3	$185.95	6.662%	$198.338	$198.34	$198.35	$198.30
Purchase #4	$211.34	9.638%	$231.7089	$231.71	$231.70	$231.70
Purchase #5	$63.77	4.822%	$66.845	$66.85	$66.85	$66.80
Purchase #6	$141.54	7.227%	$151.7691	$151.77	$151.75	$151.80
Purchase #7	$231.71	13.152%	$262.1845	$262.18	$262.20	$262.20
7 purchase totals =	$1,128.82		$1,217.9087	$1,217.91	$1,217.90	$1,217.90