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	$59.81	10.421%	$66.0428	$66.04	$66.05	$66.00
Purchase #2	$124.41	8.111%	$134.5009	$134.50	$134.50	$134.50
Purchase #3	$52.64	3.109%	$54.2766	$54.28	$54.30	$54.30
Purchase #4	$167.42	3.166%	$172.7205	$172.72	$172.70	$172.70
Purchase #5	$114.61	3.344%	$118.4426	$118.44	$118.45	$118.40
Purchase #6	$41.55	10.173%	$45.7769	$45.78	$45.80	$45.80
Purchase #7	$75.48	7.177%	$80.8972	$80.90	$80.90	$80.90
7 purchase totals =	$635.92		$672.6575	$672.66	$672.70	$672.60