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	$230.74	11.161%	$256.4929	$256.49	$256.50	$256.50
Purchase #2	$100.35	11.781%	$112.1722	$112.17	$112.15	$112.20
Purchase #3	$155.39	6.505%	$165.4981	$165.50	$165.50	$165.50
Purchase #4	$242.37	5.741%	$256.2845	$256.28	$256.30	$256.30
Purchase #5	$94.40	13.290%	$106.9458	$106.95	$106.95	$106.90
Purchase #6	$33.68	10.371%	$37.173	$37.17	$37.15	$37.20
Purchase #7	$13.86	12.138%	$15.5423	$15.54	$15.55	$15.50
7 purchase totals =	$870.79		$950.1088	$950.10	$950.10	$950.10