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	$26.79	13.664%	$30.4506	$30.45	$30.45	$30.50
Purchase #2	$103.78	12.425%	$116.6747	$116.67	$116.65	$116.70
Purchase #3	$243.43	13.142%	$275.4216	$275.42	$275.40	$275.40
Purchase #4	$90.67	11.314%	$100.9284	$100.93	$100.95	$100.90
Purchase #5	$123.73	13.106%	$139.9461	$139.95	$139.95	$139.90
Purchase #6	$101.60	8.551%	$110.2878	$110.29	$110.30	$110.30
Purchase #7	$207.48	7.484%	$223.0078	$223.01	$223.00	$223.00
7 purchase totals =	$897.48		$996.7170	$996.72	$996.70	$996.70