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	$173.48	3.527%	$179.5986	$179.60	$179.60	$179.60
Purchase #2	$34.55	8.620%	$37.5282	$37.53	$37.55	$37.50
Purchase #3	$92.29	12.484%	$103.8115	$103.81	$103.80	$103.80
Purchase #4	$137.96	7.603%	$148.4491	$148.45	$148.45	$148.40
Purchase #5	$48.68	4.504%	$50.8725	$50.87	$50.85	$50.90
Purchase #6	$14.66	4.117%	$15.2636	$15.26	$15.25	$15.30
Purchase #7	$245.48	4.277%	$255.9792	$255.98	$256.00	$256.00
7 purchase totals =	$747.10		$791.5027	$791.50	$791.50	$791.50