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	$121.63	13.108%	$137.5733	$137.57	$137.55	$137.60
Purchase #2	$40.30	8.420%	$43.6933	$43.69	$43.70	$43.70
Purchase #3	$10.41	3.587%	$10.7834	$10.78	$10.80	$10.80
Purchase #4	$218.48	4.177%	$227.6059	$227.61	$227.60	$227.60
Purchase #5	$138.39	9.862%	$152.038	$152.04	$152.05	$152.00
Purchase #6	$46.62	10.711%	$51.6135	$51.61	$51.60	$51.60
Purchase #7	$246.59	12.449%	$277.288	$277.29	$277.30	$277.30
7 purchase totals =	$822.42		$900.5954	$900.59	$900.60	$900.60