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	$218.79	4.525%	$228.6902	$228.69	$228.70	$228.70
Purchase #2	$159.76	7.635%	$171.9577	$171.96	$171.95	$172.00
Purchase #3	$225.50	13.123%	$255.0924	$255.09	$255.10	$255.10
Purchase #4	$7.65	8.657%	$8.3123	$8.31	$8.30	$8.30
Purchase #5	$40.54	5.238%	$42.6635	$42.66	$42.65	$42.70
Purchase #6	$172.25	10.520%	$190.3707	$190.37	$190.35	$190.40
Purchase #7	$175.93	4.472%	$183.7976	$183.80	$183.80	$183.80
7 purchase totals =	$1,000.42		$1,080.8844	$1,080.88	$1,080.85	$1,081.00