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	$227.63	12.749%	$256.6505	$256.65	$256.65	$256.70
Purchase #2	$137.83	7.652%	$148.3768	$148.38	$148.40	$148.40
Purchase #3	$237.47	13.293%	$269.0369	$269.04	$269.05	$269.00
Purchase #4	$84.59	12.825%	$95.4387	$95.44	$95.45	$95.40
Purchase #5	$82.61	3.576%	$85.5641	$85.56	$85.55	$85.60
Purchase #6	$82.32	4.402%	$85.9437	$85.94	$85.95	$85.90
Purchase #7	$10.40	3.716%	$10.7865	$10.79	$10.80	$10.80
7 purchase totals =	$862.85		$951.7972	$951.80	$951.85	$951.80