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	$65.59	3.122%	$67.6377	$67.64	$67.65	$67.60
Purchase #2	$18.62	7.679%	$20.0498	$20.05	$20.05	$20.00
Purchase #3	$74.78	7.472%	$80.3676	$80.37	$80.35	$80.40
Purchase #4	$222.87	4.772%	$233.5054	$233.51	$233.50	$233.50
Purchase #5	$183.96	6.493%	$195.9045	$195.90	$195.90	$195.90
Purchase #6	$235.27	6.587%	$250.7672	$250.77	$250.75	$250.80
Purchase #7	$29.28	12.259%	$32.8694	$32.87	$32.85	$32.90
7 purchase totals =	$830.37		$881.1016	$881.11	$881.05	$881.10