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	$247.82	13.602%	$281.5285	$281.53	$281.55	$281.50
Purchase #2	$125.48	5.773%	$132.724	$132.72	$132.70	$132.70
Purchase #3	$57.78	7.116%	$61.8916	$61.89	$61.90	$61.90
Purchase #4	$140.40	7.493%	$150.9202	$150.92	$150.90	$150.90
Purchase #5	$228.58	7.290%	$245.2435	$245.24	$245.25	$245.20
Purchase #6	$198.74	11.436%	$221.4679	$221.47	$221.45	$221.50
Purchase #7	$213.96	11.863%	$239.3421	$239.34	$239.35	$239.30
7 purchase totals =	$1,212.76		$1,333.1178	$1,333.11	$1,333.10	$1,333.00