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	$140.85	10.139%	$155.1308	$155.13	$155.15	$155.10
Purchase #2	$83.52	5.297%	$87.9441	$87.94	$87.95	$87.90
Purchase #3	$187.55	4.822%	$196.5937	$196.59	$196.60	$196.60
Purchase #4	$41.85	13.824%	$47.6353	$47.64	$47.65	$47.60
Purchase #5	$33.43	10.495%	$36.9385	$36.94	$36.95	$36.90
Purchase #6	$220.86	8.861%	$240.4304	$240.43	$240.45	$240.40
Purchase #7	$123.50	6.503%	$131.5312	$131.53	$131.55	$131.50
7 purchase totals =	$831.56		$896.2040	$896.20	$896.30	$896.00