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	$204.81	6.768%	$218.6715	$218.67	$218.65	$218.70
Purchase #2	$250.50	11.590%	$279.533	$279.53	$279.55	$279.50
Purchase #3	$180.59	5.140%	$189.8723	$189.87	$189.85	$189.90
Purchase #4	$144.59	5.796%	$152.9704	$152.97	$152.95	$153.00
Purchase #5	$140.80	10.317%	$155.3263	$155.33	$155.35	$155.30
Purchase #6	$214.54	3.806%	$222.7054	$222.71	$222.70	$222.70
Purchase #7	$165.42	9.307%	$180.8156	$180.82	$180.80	$180.80
7 purchase totals =	$1,301.25		$1,399.8945	$1,399.90	$1,399.85	$1,399.90