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	$159.39	12.362%	$179.0938	$179.09	$179.10	$179.10
Purchase #2	$176.56	7.341%	$189.5213	$189.52	$189.50	$189.50
Purchase #3	$81.79	9.618%	$89.6566	$89.66	$89.65	$89.70
Purchase #4	$192.52	8.138%	$208.1873	$208.19	$208.20	$208.20
Purchase #5	$200.79	8.284%	$217.4234	$217.42	$217.40	$217.40
Purchase #6	$238.29	7.359%	$255.8258	$255.83	$255.85	$255.80
Purchase #7	$7.26	9.517%	$7.9509	$7.95	$7.95	$8.00
7 purchase totals =	$1,056.60		$1,147.6591	$1,147.66	$1,147.65	$1,147.70