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	$37.58	12.630%	$42.3264	$42.33	$42.35	$42.30
Purchase #2	$66.63	10.328%	$73.5115	$73.51	$73.50	$73.50
Purchase #3	$172.42	3.404%	$178.2892	$178.29	$178.30	$178.30
Purchase #4	$238.74	13.286%	$270.459	$270.46	$270.45	$270.50
Purchase #5	$11.52	6.198%	$12.234	$12.23	$12.25	$12.20
Purchase #6	$140.60	6.363%	$149.5464	$149.55	$149.55	$149.50
Purchase #7	$205.60	5.663%	$217.2431	$217.24	$217.25	$217.20
7 purchase totals =	$873.09		$943.6096	$943.61	$943.65	$943.50