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	$146.41	8.144%	$158.3336	$158.33	$158.35	$158.30
Purchase #2	$78.81	5.504%	$83.1477	$83.15	$83.15	$83.10
Purchase #3	$169.93	9.367%	$185.8473	$185.85	$185.85	$185.80
Purchase #4	$35.75	10.727%	$39.5849	$39.58	$39.60	$39.60
Purchase #5	$201.85	7.263%	$216.5104	$216.51	$216.50	$216.50
Purchase #6	$97.85	4.774%	$102.5214	$102.52	$102.50	$102.50
Purchase #7	$78.77	3.741%	$81.7168	$81.72	$81.70	$81.70
7 purchase totals =	$809.37		$867.6621	$867.66	$867.65	$867.50