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	$140.74	7.754%	$151.653	$151.65	$151.65	$151.70
Purchase #2	$146.60	9.452%	$160.4566	$160.46	$160.45	$160.50
Purchase #3	$57.26	5.535%	$60.4293	$60.43	$60.45	$60.40
Purchase #4	$53.41	12.668%	$60.176	$60.18	$60.20	$60.20
Purchase #5	$162.45	11.220%	$180.6769	$180.68	$180.70	$180.70
Purchase #6	$55.85	6.428%	$59.44	$59.44	$59.45	$59.40
Purchase #7	$75.40	9.351%	$82.4507	$82.45	$82.45	$82.50
7 purchase totals =	$691.71		$755.2825	$755.29	$755.35	$755.40