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	$153.66	3.844%	$159.5667	$159.57	$159.55	$159.60
Purchase #2	$71.74	9.513%	$78.5646	$78.56	$78.55	$78.60
Purchase #3	$47.94	4.581%	$50.1361	$50.14	$50.15	$50.10
Purchase #4	$56.71	8.385%	$61.4651	$61.47	$61.45	$61.50
Purchase #5	$149.38	11.508%	$166.5707	$166.57	$166.55	$166.60
Purchase #6	$136.31	5.843%	$144.2746	$144.27	$144.25	$144.30
Purchase #7	$209.35	13.594%	$237.809	$237.81	$237.80	$237.80
7 purchase totals =	$825.09		$898.3868	$898.39	$898.30	$898.50