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	$34.87	4.326%	$36.3785	$36.38	$36.40	$36.40
Purchase #2	$26.81	13.318%	$30.3806	$30.38	$30.40	$30.40
Purchase #3	$145.91	3.673%	$151.2693	$151.27	$151.25	$151.30
Purchase #4	$60.64	11.203%	$67.4335	$67.43	$67.45	$67.40
Purchase #5	$86.39	5.210%	$90.8909	$90.89	$90.90	$90.90
Purchase #6	$217.90	11.190%	$242.283	$242.28	$242.30	$242.30
Purchase #7	$40.62	7.599%	$43.7067	$43.71	$43.70	$43.70
7 purchase totals =	$613.14		$662.3425	$662.34	$662.40	$662.40