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	$43.81	10.419%	$48.3746	$48.37	$48.35	$48.40
Purchase #2	$84.47	6.387%	$89.8651	$89.87	$89.85	$89.90
Purchase #3	$62.73	7.869%	$67.6662	$67.67	$67.65	$67.70
Purchase #4	$19.85	13.164%	$22.4631	$22.46	$22.45	$22.50
Purchase #5	$222.34	4.273%	$231.8406	$231.84	$231.85	$231.80
Purchase #6	$50.91	11.754%	$56.894	$56.89	$56.90	$56.90
Purchase #7	$112.28	10.827%	$124.4366	$124.44	$124.45	$124.40
7 purchase totals =	$596.39		$641.5402	$641.54	$641.50	$641.60