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	$32.78	4.843%	$34.3675	$34.37	$34.35	$34.40
Purchase #2	$156.36	12.302%	$175.5954	$175.60	$175.60	$175.60
Purchase #3	$153.86	3.679%	$159.5205	$159.52	$159.50	$159.50
Purchase #4	$223.92	12.637%	$252.2168	$252.22	$252.20	$252.20
Purchase #5	$243.44	12.460%	$273.7726	$273.77	$273.75	$273.80
Purchase #6	$53.71	11.174%	$59.7116	$59.71	$59.70	$59.70
Purchase #7	$158.72	5.863%	$168.0258	$168.03	$168.05	$168.00
7 purchase totals =	$1,022.79		$1,123.2102	$1,123.22	$1,123.15	$1,123.20