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	$121.61	12.765%	$137.1335	$137.13	$137.15	$137.10
Purchase #2	$48.71	7.840%	$52.5289	$52.53	$52.55	$52.50
Purchase #3	$84.54	8.208%	$91.479	$91.48	$91.50	$91.50
Purchase #4	$15.39	10.816%	$17.0546	$17.05	$17.05	$17.10
Purchase #5	$138.41	8.705%	$150.4586	$150.46	$150.45	$150.50
Purchase #6	$221.53	9.454%	$242.4734	$242.47	$242.45	$242.50
Purchase #7	$37.62	5.846%	$39.8193	$39.82	$39.80	$39.80
7 purchase totals =	$667.81		$730.9473	$730.94	$730.95	$731.00