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	$36.27	3.732%	$37.6236	$37.62	$37.60	$37.60
Purchase #2	$34.53	8.267%	$37.3846	$37.38	$37.40	$37.40
Purchase #3	$170.45	9.599%	$186.8115	$186.81	$186.80	$186.80
Purchase #4	$120.68	6.638%	$128.6907	$128.69	$128.70	$128.70
Purchase #5	$12.51	12.502%	$14.074	$14.07	$14.05	$14.10
Purchase #6	$233.59	7.195%	$250.3968	$250.40	$250.40	$250.40
Purchase #7	$77.52	9.770%	$85.0937	$85.09	$85.10	$85.10
7 purchase totals =	$685.55		$740.0749	$740.06	$740.05	$740.10