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	$201.59	12.758%	$227.3089	$227.31	$227.30	$227.30
Purchase #2	$53.56	6.622%	$57.1067	$57.11	$57.10	$57.10
Purchase #3	$64.98	11.197%	$72.2558	$72.26	$72.25	$72.30
Purchase #4	$50.73	7.576%	$54.5733	$54.57	$54.55	$54.60
Purchase #5	$57.91	9.553%	$63.4421	$63.44	$63.45	$63.40
Purchase #6	$224.63	13.540%	$255.0449	$255.04	$255.05	$255.00
Purchase #7	$62.84	6.405%	$66.8649	$66.86	$66.85	$66.90
7 purchase totals =	$716.24		$796.5966	$796.59	$796.55	$796.60