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	$146.67	3.522%	$151.8357	$151.84	$151.85	$151.80
Purchase #2	$196.78	13.563%	$223.4693	$223.47	$223.45	$223.50
Purchase #3	$48.35	11.158%	$53.7449	$53.74	$53.75	$53.70
Purchase #4	$56.85	12.480%	$63.9449	$63.94	$63.95	$63.90
Purchase #5	$115.35	11.356%	$128.4491	$128.45	$128.45	$128.40
Purchase #6	$158.55	7.672%	$170.714	$170.71	$170.70	$170.70
Purchase #7	$172.85	9.477%	$189.231	$189.23	$189.25	$189.20
7 purchase totals =	$895.40		$981.3889	$981.38	$981.40	$981.20