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	$131.58	9.803%	$144.4788	$144.48	$144.50	$144.50
Purchase #2	$129.37	8.860%	$140.8322	$140.83	$140.85	$140.80
Purchase #3	$66.95	5.425%	$70.582	$70.58	$70.60	$70.60
Purchase #4	$44.35	4.759%	$46.4606	$46.46	$46.45	$46.50
Purchase #5	$56.49	7.434%	$60.6895	$60.69	$60.70	$60.70
Purchase #6	$42.49	7.253%	$45.5718	$45.57	$45.55	$45.60
Purchase #7	$19.34	4.684%	$20.2459	$20.25	$20.25	$20.20
7 purchase totals =	$490.57		$528.8608	$528.86	$528.90	$528.90