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	$238.26	3.762%	$247.2233	$247.22	$247.20	$247.20
Purchase #2	$244.38	4.691%	$255.8439	$255.84	$255.85	$255.80
Purchase #3	$186.41	6.444%	$198.4223	$198.42	$198.40	$198.40
Purchase #4	$215.76	4.544%	$225.5641	$225.56	$225.55	$225.60
Purchase #5	$171.46	11.117%	$190.5212	$190.52	$190.50	$190.50
Purchase #6	$50.25	11.743%	$56.1509	$56.15	$56.15	$56.20
Purchase #7	$58.38	13.490%	$66.2555	$66.26	$66.25	$66.30
7 purchase totals =	$1,164.90		$1,239.9812	$1,239.97	$1,239.90	$1,240.00