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	$135.63	11.690%	$151.4851	$151.49	$151.50	$151.50
Purchase #2	$229.54	11.771%	$256.5592	$256.56	$256.55	$256.60
Purchase #3	$188.76	13.828%	$214.8617	$214.86	$214.85	$214.90
Purchase #4	$19.34	8.665%	$21.0158	$21.02	$21.00	$21.00
Purchase #5	$52.32	13.141%	$59.1954	$59.20	$59.20	$59.20
Purchase #6	$57.27	3.549%	$59.3025	$59.30	$59.30	$59.30
Purchase #7	$107.74	4.605%	$112.7014	$112.70	$112.70	$112.70
7 purchase totals =	$790.60		$875.1211	$875.13	$875.10	$875.20