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	$15.97	6.680%	$17.0368	$17.04	$17.05	$17.00
Purchase #2	$56.63	12.388%	$63.6453	$63.65	$63.65	$63.60
Purchase #3	$179.82	9.472%	$196.8526	$196.85	$196.85	$196.90
Purchase #4	$159.73	3.855%	$165.8876	$165.89	$165.90	$165.90
Purchase #5	$139.85	12.352%	$157.1243	$157.12	$157.10	$157.10
Purchase #6	$227.65	12.757%	$256.6913	$256.69	$256.70	$256.70
Purchase #7	$162.43	10.682%	$179.7808	$179.78	$179.80	$179.80
7 purchase totals =	$942.08		$1,037.0187	$1,037.02	$1,037.05	$1,037.00