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	$73.44	9.707%	$80.5688	$80.57	$80.55	$80.60
Purchase #2	$40.36	13.189%	$45.6831	$45.68	$45.70	$45.70
Purchase #3	$86.64	9.656%	$95.006	$95.01	$95.00	$95.00
Purchase #4	$206.68	7.148%	$221.4535	$221.45	$221.45	$221.50
Purchase #5	$44.82	13.453%	$50.8496	$50.85	$50.85	$50.80
Purchase #6	$95.83	4.204%	$99.8587	$99.86	$99.85	$99.90
Purchase #7	$152.78	11.782%	$170.7805	$170.78	$170.80	$170.80
7 purchase totals =	$700.55		$764.2002	$764.20	$764.20	$764.30