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	$29.57	3.504%	$30.6061	$30.61	$30.60	$30.60
Purchase #2	$40.72	3.242%	$42.0401	$42.04	$42.05	$42.00
Purchase #3	$63.60	5.863%	$67.3289	$67.33	$67.35	$67.30
Purchase #4	$81.34	7.449%	$87.399	$87.40	$87.40	$87.40
Purchase #5	$192.27	12.470%	$216.2461	$216.25	$216.25	$216.20
Purchase #6	$148.78	6.105%	$157.863	$157.86	$157.85	$157.90
Purchase #7	$128.80	8.175%	$139.3294	$139.33	$139.35	$139.30
7 purchase totals =	$685.08		$740.8126	$740.82	$740.85	$740.70