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	$37.96	4.167%	$39.5418	$39.54	$39.55	$39.50
Purchase #2	$69.29	13.849%	$78.886	$78.89	$78.90	$78.90
Purchase #3	$103.60	12.476%	$116.5251	$116.53	$116.55	$116.50
Purchase #4	$137.61	9.253%	$150.3431	$150.34	$150.35	$150.30
Purchase #5	$137.61	6.497%	$146.5505	$146.55	$146.55	$146.60
Purchase #6	$246.67	13.837%	$280.8017	$280.80	$280.80	$280.80
Purchase #7	$183.89	8.663%	$199.8204	$199.82	$199.80	$199.80
7 purchase totals =	$916.63		$1,012.4686	$1,012.47	$1,012.50	$1,012.40