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	$182.75	3.167%	$188.5377	$188.54	$188.55	$188.50
Purchase #2	$122.45	7.612%	$131.7709	$131.77	$131.75	$131.80
Purchase #3	$29.90	9.250%	$32.6658	$32.67	$32.65	$32.70
Purchase #4	$39.52	8.684%	$42.9519	$42.95	$42.95	$43.00
Purchase #5	$34.53	8.491%	$37.4619	$37.46	$37.45	$37.50
Purchase #6	$126.95	8.730%	$138.0327	$138.03	$138.05	$138.00
Purchase #7	$34.47	11.259%	$38.351	$38.35	$38.35	$38.40
7 purchase totals =	$570.57		$609.7719	$609.77	$609.75	$609.90