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	$175.47	5.609%	$185.3121	$185.31	$185.30	$185.30
Purchase #2	$72.45	7.847%	$78.1352	$78.14	$78.15	$78.10
Purchase #3	$12.59	13.484%	$14.2876	$14.29	$14.30	$14.30
Purchase #4	$132.97	6.648%	$141.8098	$141.81	$141.80	$141.80
Purchase #5	$67.86	9.337%	$74.1961	$74.20	$74.20	$74.20
Purchase #6	$56.25	9.327%	$61.4964	$61.50	$61.50	$61.50
Purchase #7	$83.40	8.862%	$90.7909	$90.79	$90.80	$90.80
7 purchase totals =	$600.99		$646.0281	$646.04	$646.05	$646.00