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	$127.72	10.570%	$141.22	$141.22	$141.20	$141.20
Purchase #2	$211.58	3.725%	$219.4614	$219.46	$219.45	$219.50
Purchase #3	$62.82	6.309%	$66.7833	$66.78	$66.80	$66.80
Purchase #4	$220.88	7.727%	$237.9474	$237.95	$237.95	$237.90
Purchase #5	$185.81	7.547%	$199.8331	$199.83	$199.85	$199.80
Purchase #6	$213.48	6.710%	$227.8045	$227.80	$227.80	$227.80
Purchase #7	$141.94	7.363%	$152.391	$152.39	$152.40	$152.40
7 purchase totals =	$1,164.23		$1,245.4407	$1,245.43	$1,245.45	$1,245.40