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	$236.50	8.103%	$255.6636	$255.66	$255.65	$255.70
Purchase #2	$89.86	10.376%	$99.1839	$99.18	$99.20	$99.20
Purchase #3	$89.61	10.737%	$99.2314	$99.23	$99.25	$99.20
Purchase #4	$9.88	3.760%	$10.2515	$10.25	$10.25	$10.30
Purchase #5	$15.67	13.785%	$17.8301	$17.83	$17.85	$17.80
Purchase #6	$241.74	13.677%	$274.8028	$274.80	$274.80	$274.80
Purchase #7	$5.73	12.551%	$6.4492	$6.45	$6.45	$6.40
7 purchase totals =	$688.99		$763.4125	$763.40	$763.45	$763.40