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	$112.93	13.657%	$128.3529	$128.35	$128.35	$128.40
Purchase #2	$38.82	13.672%	$44.1275	$44.13	$44.15	$44.10
Purchase #3	$176.93	4.601%	$185.0705	$185.07	$185.05	$185.10
Purchase #4	$136.90	13.806%	$155.8004	$155.80	$155.80	$155.80
Purchase #5	$17.54	11.787%	$19.6074	$19.61	$19.60	$19.60
Purchase #6	$57.35	5.750%	$60.6476	$60.65	$60.65	$60.60
Purchase #7	$68.32	4.821%	$71.6137	$71.61	$71.60	$71.60
7 purchase totals =	$608.79		$665.2200	$665.22	$665.20	$665.20