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	$37.86	7.422%	$40.67	$40.67	$40.65	$40.70
Purchase #2	$150.71	10.501%	$166.5361	$166.54	$166.55	$166.50
Purchase #3	$158.88	7.610%	$170.9708	$170.97	$170.95	$171.00
Purchase #4	$180.58	10.117%	$198.8493	$198.85	$198.85	$198.80
Purchase #5	$96.74	13.487%	$109.7873	$109.79	$109.80	$109.80
Purchase #6	$120.65	13.597%	$137.0548	$137.05	$137.05	$137.10
Purchase #7	$70.50	11.844%	$78.85	$78.85	$78.85	$78.90
7 purchase totals =	$815.92		$902.7183	$902.72	$902.70	$902.80