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	$247.40	5.181%	$260.2178	$260.22	$260.20	$260.20
Purchase #2	$248.70	10.459%	$274.7115	$274.71	$274.70	$274.70
Purchase #3	$166.39	13.619%	$189.0507	$189.05	$189.05	$189.10
Purchase #4	$53.89	9.822%	$59.1831	$59.18	$59.20	$59.20
Purchase #5	$13.95	10.694%	$15.4418	$15.44	$15.45	$15.40
Purchase #6	$139.83	9.119%	$152.5811	$152.58	$152.60	$152.60
Purchase #7	$177.53	12.831%	$200.3089	$200.31	$200.30	$200.30
7 purchase totals =	$1,047.69		$1,151.4949	$1,151.49	$1,151.50	$1,151.50