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	$28.38	8.708%	$30.8513	$30.85	$30.85	$30.90
Purchase #2	$36.82	10.359%	$40.6342	$40.63	$40.65	$40.60
Purchase #3	$127.50	10.309%	$140.644	$140.64	$140.65	$140.60
Purchase #4	$117.58	5.815%	$124.4173	$124.42	$124.40	$124.40
Purchase #5	$63.72	5.785%	$67.4062	$67.41	$67.40	$67.40
Purchase #6	$66.58	4.369%	$69.4889	$69.49	$69.50	$69.50
Purchase #7	$65.27	11.482%	$72.7643	$72.76	$72.75	$72.80
7 purchase totals =	$505.85		$546.2062	$546.20	$546.20	$546.20