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	$113.73	9.511%	$124.5469	$124.55	$124.55	$124.50
Purchase #2	$65.59	12.584%	$73.8438	$73.84	$73.85	$73.80
Purchase #3	$73.78	11.763%	$82.4587	$82.46	$82.45	$82.50
Purchase #4	$71.52	7.631%	$76.9777	$76.98	$77.00	$77.00
Purchase #5	$82.25	9.839%	$90.3426	$90.34	$90.35	$90.30
Purchase #6	$45.43	6.271%	$48.2789	$48.28	$48.30	$48.30
Purchase #7	$193.53	10.482%	$213.8158	$213.82	$213.80	$213.80
7 purchase totals =	$645.83		$710.2644	$710.27	$710.30	$710.20