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	$213.72	13.660%	$242.9142	$242.91	$242.90	$242.90
Purchase #2	$169.33	12.275%	$190.1153	$190.12	$190.10	$190.10
Purchase #3	$214.59	4.604%	$224.4697	$224.47	$224.45	$224.50
Purchase #4	$45.44	12.309%	$51.0332	$51.03	$51.05	$51.00
Purchase #5	$121.25	13.434%	$137.5387	$137.54	$137.55	$137.50
Purchase #6	$30.41	4.785%	$31.8651	$31.87	$31.85	$31.90
Purchase #7	$226.82	8.388%	$245.8457	$245.85	$245.85	$245.80
7 purchase totals =	$1,021.56		$1,123.7819	$1,123.79	$1,123.75	$1,123.70