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	$120.80	13.651%	$137.2904	$137.29	$137.30	$137.30
Purchase #2	$78.59	6.655%	$83.8202	$83.82	$83.80	$83.80
Purchase #3	$19.73	7.579%	$21.2253	$21.23	$21.25	$21.20
Purchase #4	$138.46	12.567%	$155.8603	$155.86	$155.85	$155.90
Purchase #5	$195.49	13.400%	$221.6857	$221.69	$221.70	$221.70
Purchase #6	$122.53	7.680%	$131.9403	$131.94	$131.95	$131.90
Purchase #7	$103.26	10.667%	$114.2747	$114.27	$114.25	$114.30
7 purchase totals =	$778.86		$866.0969	$866.10	$866.10	$866.10