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	$134.85	12.500%	$151.7063	$151.71	$151.70	$151.70
Purchase #2	$30.89	10.853%	$34.2425	$34.24	$34.25	$34.20
Purchase #3	$78.57	8.274%	$85.0709	$85.07	$85.05	$85.10
Purchase #4	$107.46	13.168%	$121.6103	$121.61	$121.60	$121.60
Purchase #5	$239.63	13.767%	$272.6199	$272.62	$272.60	$272.60
Purchase #6	$42.93	6.557%	$45.7449	$45.74	$45.75	$45.70
Purchase #7	$139.38	13.800%	$158.6144	$158.61	$158.60	$158.60
7 purchase totals =	$773.71		$869.6092	$869.60	$869.55	$869.50