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	$67.65	3.624%	$70.1016	$70.10	$70.10	$70.10
Purchase #2	$19.78	13.574%	$22.4649	$22.46	$22.45	$22.50
Purchase #3	$91.53	13.279%	$103.6843	$103.68	$103.70	$103.70
Purchase #4	$11.66	13.503%	$13.2344	$13.23	$13.25	$13.20
Purchase #5	$37.29	5.856%	$39.4737	$39.47	$39.45	$39.50
Purchase #6	$63.31	5.485%	$66.7826	$66.78	$66.80	$66.80
Purchase #7	$23.80	3.825%	$24.7104	$24.71	$24.70	$24.70
7 purchase totals =	$315.02		$340.4519	$340.43	$340.45	$340.50