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	$240.82	6.251%	$255.8737	$255.87	$255.85	$255.90
Purchase #2	$121.57	7.734%	$130.9722	$130.97	$130.95	$131.00
Purchase #3	$149.82	12.436%	$168.4516	$168.45	$168.45	$168.50
Purchase #4	$155.74	11.450%	$173.5722	$173.57	$173.55	$173.60
Purchase #5	$136.97	13.789%	$155.8568	$155.86	$155.85	$155.90
Purchase #6	$7.36	7.763%	$7.9314	$7.93	$7.95	$7.90
Purchase #7	$14.60	4.312%	$15.2296	$15.23	$15.25	$15.20
7 purchase totals =	$826.88		$907.8875	$907.88	$907.85	$908.00