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	$109.57	5.457%	$115.5492	$115.55	$115.55	$115.50
Purchase #2	$52.55	13.344%	$59.5623	$59.56	$59.55	$59.60
Purchase #3	$59.37	11.399%	$66.1376	$66.14	$66.15	$66.10
Purchase #4	$48.74	4.105%	$50.7408	$50.74	$50.75	$50.70
Purchase #5	$75.46	10.487%	$83.3735	$83.37	$83.35	$83.40
Purchase #6	$104.72	7.852%	$112.9426	$112.94	$112.95	$112.90
Purchase #7	$62.94	8.525%	$68.3056	$68.31	$68.30	$68.30
7 purchase totals =	$513.35		$556.6116	$556.61	$556.60	$556.50