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	$39.78	8.164%	$43.0276	$43.03	$43.05	$43.00
Purchase #2	$222.93	10.750%	$246.895	$246.90	$246.90	$246.90
Purchase #3	$34.51	9.607%	$37.8254	$37.83	$37.85	$37.80
Purchase #4	$26.50	9.634%	$29.053	$29.05	$29.05	$29.10
Purchase #5	$125.94	12.330%	$141.4684	$141.47	$141.45	$141.50
Purchase #6	$221.73	4.223%	$231.0937	$231.09	$231.10	$231.10
Purchase #7	$36.47	13.695%	$41.4646	$41.46	$41.45	$41.50
7 purchase totals =	$707.86		$770.8277	$770.83	$770.85	$770.90