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	$136.53	6.398%	$145.2652	$145.27	$145.25	$145.30
Purchase #2	$243.72	11.852%	$272.6057	$272.61	$272.60	$272.60
Purchase #3	$28.90	10.517%	$31.9394	$31.94	$31.95	$31.90
Purchase #4	$205.53	7.267%	$220.4659	$220.47	$220.45	$220.50
Purchase #5	$134.92	3.413%	$139.5248	$139.52	$139.50	$139.50
Purchase #6	$107.70	4.161%	$112.1814	$112.18	$112.20	$112.20
Purchase #7	$113.89	6.702%	$121.5229	$121.52	$121.50	$121.50
7 purchase totals =	$971.19		$1,043.5053	$1,043.51	$1,043.45	$1,043.50