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	$60.75	9.840%	$66.7278	$66.73	$66.75	$66.70
Purchase #2	$141.70	13.152%	$160.3364	$160.34	$160.35	$160.30
Purchase #3	$221.38	13.174%	$250.5446	$250.54	$250.55	$250.50
Purchase #4	$63.47	5.500%	$66.9609	$66.96	$66.95	$67.00
Purchase #5	$140.74	8.593%	$152.8338	$152.83	$152.85	$152.80
Purchase #6	$146.47	13.862%	$166.7737	$166.77	$166.75	$166.80
Purchase #7	$54.74	5.557%	$57.7819	$57.78	$57.80	$57.80
7 purchase totals =	$829.25		$921.9591	$921.95	$922.00	$921.90