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	$134.51	13.604%	$152.8087	$152.81	$152.80	$152.80
Purchase #2	$13.54	13.517%	$15.3702	$15.37	$15.35	$15.40
Purchase #3	$141.53	8.611%	$153.7171	$153.72	$153.70	$153.70
Purchase #4	$163.90	13.165%	$185.4774	$185.48	$185.50	$185.50
Purchase #5	$157.67	10.717%	$174.5675	$174.57	$174.55	$174.60
Purchase #6	$16.79	6.291%	$17.8463	$17.85	$17.85	$17.80
Purchase #7	$247.87	11.700%	$276.8708	$276.87	$276.85	$276.90
7 purchase totals =	$875.81		$976.6580	$976.67	$976.60	$976.70