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	$82.38	11.315%	$91.7013	$91.70	$91.70	$91.70
Purchase #2	$54.47	8.578%	$59.1424	$59.14	$59.15	$59.10
Purchase #3	$143.78	12.385%	$161.5872	$161.59	$161.60	$161.60
Purchase #4	$157.63	13.723%	$179.2616	$179.26	$179.25	$179.30
Purchase #5	$76.93	11.510%	$85.7846	$85.78	$85.80	$85.80
Purchase #6	$187.82	11.655%	$209.7104	$209.71	$209.70	$209.70
Purchase #7	$95.61	10.591%	$105.7361	$105.74	$105.75	$105.70
7 purchase totals =	$798.62		$892.9236	$892.92	$892.95	$892.90