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	$134.27	4.432%	$140.2208	$140.22	$140.20	$140.20
Purchase #2	$70.56	7.842%	$76.0933	$76.09	$76.10	$76.10
Purchase #3	$250.54	8.476%	$271.7758	$271.78	$271.80	$271.80
Purchase #4	$45.58	7.282%	$48.8991	$48.90	$48.90	$48.90
Purchase #5	$54.39	13.720%	$61.8523	$61.85	$61.85	$61.90
Purchase #6	$60.80	9.185%	$66.3845	$66.38	$66.40	$66.40
Purchase #7	$140.76	12.825%	$158.8125	$158.81	$158.80	$158.80
7 purchase totals =	$756.90		$824.0383	$824.03	$824.05	$824.10