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	4.870%	$259.8888	$259.89	$259.90	$259.90
Purchase #2	$82.42	3.331%	$85.1654	$85.17	$85.15	$85.20
Purchase #3	$208.60	8.207%	$225.7198	$225.72	$225.70	$225.70
Purchase #4	$90.31	10.105%	$99.4358	$99.44	$99.45	$99.40
Purchase #5	$222.57	9.680%	$244.1148	$244.11	$244.10	$244.10
Purchase #6	$112.92	13.871%	$128.5831	$128.58	$128.60	$128.60
Purchase #7	$169.97	11.538%	$189.5811	$189.58	$189.60	$189.60
7 purchase totals =	$1,134.61		$1,232.4888	$1,232.49	$1,232.50	$1,232.50