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	$47.71	11.657%	$53.2716	$53.27	$53.25	$53.30
Purchase #2	$124.36	12.495%	$139.8988	$139.90	$139.90	$139.90
Purchase #3	$52.65	12.635%	$59.3023	$59.30	$59.30	$59.30
Purchase #4	$9.37	10.837%	$10.3854	$10.39	$10.40	$10.40
Purchase #5	$65.26	8.466%	$70.7849	$70.78	$70.80	$70.80
Purchase #6	$94.31	12.790%	$106.3722	$106.37	$106.35	$106.40
Purchase #7	$32.50	7.682%	$34.9967	$35.00	$35.00	$35.00
7 purchase totals =	$426.16		$475.0119	$475.01	$475.00	$475.10