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	$85.56	6.150%	$90.8219	$90.82	$90.80	$90.80
Purchase #2	$240.30	12.203%	$269.6238	$269.62	$269.60	$269.60
Purchase #3	$194.66	5.574%	$205.5103	$205.51	$205.50	$205.50
Purchase #4	$126.78	8.372%	$137.394	$137.39	$137.40	$137.40
Purchase #5	$233.78	9.163%	$255.2013	$255.20	$255.20	$255.20
Purchase #6	$247.94	9.186%	$270.7158	$270.72	$270.70	$270.70
Purchase #7	$103.43	6.780%	$110.4426	$110.44	$110.45	$110.40
7 purchase totals =	$1,232.45		$1,339.7097	$1,339.70	$1,339.65	$1,339.60