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	$231.61	6.589%	$246.8708	$246.87	$246.85	$246.90
Purchase #2	$126.34	11.372%	$140.7074	$140.71	$140.70	$140.70
Purchase #3	$144.49	13.801%	$164.4311	$164.43	$164.45	$164.40
Purchase #4	$214.35	12.191%	$240.4814	$240.48	$240.50	$240.50
Purchase #5	$125.59	6.405%	$133.634	$133.63	$133.65	$133.60
Purchase #6	$180.81	5.373%	$190.5249	$190.52	$190.50	$190.50
Purchase #7	$81.46	11.117%	$90.5159	$90.52	$90.50	$90.50
7 purchase totals =	$1,104.65		$1,207.1655	$1,207.16	$1,207.15	$1,207.10