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	$112.95	7.110%	$120.9807	$120.98	$121.00	$121.00
Purchase #2	$18.77	8.168%	$20.3031	$20.30	$20.30	$20.30
Purchase #3	$67.42	5.531%	$71.149	$71.15	$71.15	$71.10
Purchase #4	$111.76	4.192%	$116.445	$116.45	$116.45	$116.40
Purchase #5	$21.28	12.389%	$23.9164	$23.92	$23.90	$23.90
Purchase #6	$95.85	10.243%	$105.6679	$105.67	$105.65	$105.70
Purchase #7	$30.67	7.220%	$32.8844	$32.88	$32.90	$32.90
7 purchase totals =	$458.70		$491.3465	$491.35	$491.35	$491.30