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	$208.89	7.145%	$223.8152	$223.82	$223.80	$223.80
Purchase #2	$244.76	4.255%	$255.1745	$255.17	$255.15	$255.20
Purchase #3	$131.57	9.144%	$143.6008	$143.60	$143.60	$143.60
Purchase #4	$23.55	5.525%	$24.8511	$24.85	$24.85	$24.90
Purchase #5	$43.95	4.355%	$45.864	$45.86	$45.85	$45.90
Purchase #6	$40.77	10.289%	$44.9648	$44.96	$44.95	$45.00
Purchase #7	$18.82	8.775%	$20.4715	$20.47	$20.45	$20.50
7 purchase totals =	$712.31		$758.7419	$758.73	$758.65	$758.90