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	$137.31	5.664%	$145.0872	$145.09	$145.10	$145.10
Purchase #2	$6.41	9.619%	$7.0266	$7.03	$7.05	$7.00
Purchase #3	$45.38	11.428%	$50.566	$50.57	$50.55	$50.60
Purchase #4	$37.73	7.241%	$40.462	$40.46	$40.45	$40.50
Purchase #5	$141.77	4.559%	$148.2333	$148.23	$148.25	$148.20
Purchase #6	$195.60	13.657%	$222.3131	$222.31	$222.30	$222.30
Purchase #7	$86.85	9.361%	$94.98	$94.98	$95.00	$95.00
7 purchase totals =	$651.05		$708.6682	$708.67	$708.70	$708.70