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	$63.44	4.300%	$66.1679	$66.17	$66.15	$66.20
Purchase #2	$233.30	11.402%	$259.9009	$259.90	$259.90	$259.90
Purchase #3	$33.89	7.758%	$36.5192	$36.52	$36.50	$36.50
Purchase #4	$178.42	6.241%	$189.5552	$189.56	$189.55	$189.60
Purchase #5	$144.47	9.811%	$158.644	$158.64	$158.65	$158.60
Purchase #6	$47.71	12.860%	$53.8455	$53.85	$53.85	$53.80
Purchase #7	$184.81	3.776%	$191.7884	$191.79	$191.80	$191.80
7 purchase totals =	$886.04		$956.4211	$956.43	$956.40	$956.40