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	$53.25	13.576%	$60.4792	$60.48	$60.50	$60.50
Purchase #2	$106.74	10.305%	$117.7396	$117.74	$117.75	$117.70
Purchase #3	$37.76	12.715%	$42.5612	$42.56	$42.55	$42.60
Purchase #4	$137.93	4.719%	$144.4389	$144.44	$144.45	$144.40
Purchase #5	$173.56	8.543%	$188.3872	$188.39	$188.40	$188.40
Purchase #6	$216.61	9.623%	$237.4544	$237.45	$237.45	$237.50
Purchase #7	$144.69	5.429%	$152.5452	$152.55	$152.55	$152.50
7 purchase totals =	$870.54		$943.6057	$943.61	$943.65	$943.60