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	$9.90	12.332%	$11.1209	$11.12	$11.10	$11.10
Purchase #2	$243.48	3.137%	$251.118	$251.12	$251.10	$251.10
Purchase #3	$83.28	10.233%	$91.802	$91.80	$91.80	$91.80
Purchase #4	$97.83	6.189%	$103.8847	$103.88	$103.90	$103.90
Purchase #5	$217.97	9.604%	$238.9038	$238.90	$238.90	$238.90
Purchase #6	$187.88	10.842%	$208.2499	$208.25	$208.25	$208.20
Purchase #7	$56.74	4.810%	$59.4692	$59.47	$59.45	$59.50
7 purchase totals =	$897.08		$964.5485	$964.54	$964.50	$964.50