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	$40.65	10.754%	$45.0215	$45.02	$45.00	$45.00
Purchase #2	$108.74	13.680%	$123.6156	$123.62	$123.60	$123.60
Purchase #3	$51.60	12.732%	$58.1697	$58.17	$58.15	$58.20
Purchase #4	$35.76	5.213%	$37.6242	$37.62	$37.60	$37.60
Purchase #5	$121.73	13.546%	$138.2195	$138.22	$138.20	$138.20
Purchase #6	$71.38	13.314%	$80.8835	$80.88	$80.90	$80.90
Purchase #7	$41.90	8.349%	$45.3982	$45.40	$45.40	$45.40
7 purchase totals =	$471.76		$528.9322	$528.93	$528.85	$528.90