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	$225.71	12.643%	$254.2465	$254.25	$254.25	$254.20
Purchase #2	$240.52	8.234%	$260.3244	$260.32	$260.30	$260.30
Purchase #3	$144.81	7.392%	$155.5144	$155.51	$155.50	$155.50
Purchase #4	$153.46	7.465%	$164.9158	$164.92	$164.90	$164.90
Purchase #5	$32.73	11.545%	$36.5087	$36.51	$36.50	$36.50
Purchase #6	$136.68	4.420%	$142.7213	$142.72	$142.70	$142.70
Purchase #7	$117.46	5.156%	$123.5162	$123.52	$123.50	$123.50
7 purchase totals =	$1,051.37		$1,137.7473	$1,137.75	$1,137.65	$1,137.60