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	$61.57	6.246%	$65.4157	$65.42	$65.40	$65.40
Purchase #2	$218.66	13.749%	$248.7236	$248.72	$248.70	$248.70
Purchase #3	$241.73	5.851%	$255.8736	$255.87	$255.85	$255.90
Purchase #4	$143.26	10.409%	$158.1719	$158.17	$158.15	$158.20
Purchase #5	$244.47	4.523%	$255.5274	$255.53	$255.55	$255.50
Purchase #6	$152.35	12.121%	$170.8163	$170.82	$170.80	$170.80
Purchase #7	$124.74	11.724%	$139.3645	$139.36	$139.35	$139.40
7 purchase totals =	$1,186.78		$1,293.8930	$1,293.89	$1,293.80	$1,293.90