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	$126.30	12.780%	$142.4411	$142.44	$142.45	$142.40
Purchase #2	$47.98	13.442%	$54.4295	$54.43	$54.45	$54.40
Purchase #3	$155.92	10.697%	$172.5988	$172.60	$172.60	$172.60
Purchase #4	$23.89	6.602%	$25.4672	$25.47	$25.45	$25.50
Purchase #5	$173.90	12.511%	$195.6566	$195.66	$195.65	$195.70
Purchase #6	$123.98	13.639%	$140.8896	$140.89	$140.90	$140.90
Purchase #7	$100.62	13.689%	$114.3939	$114.39	$114.40	$114.40
7 purchase totals =	$752.59		$845.8767	$845.88	$845.90	$845.90