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	$27.66	12.404%	$31.0909	$31.09	$31.10	$31.10
Purchase #2	$135.46	11.418%	$150.9268	$150.93	$150.95	$150.90
Purchase #3	$157.49	12.243%	$176.7715	$176.77	$176.75	$176.80
Purchase #4	$74.60	10.254%	$82.2495	$82.25	$82.25	$82.20
Purchase #5	$103.80	4.769%	$108.7502	$108.75	$108.75	$108.80
Purchase #6	$179.66	4.580%	$187.8884	$187.89	$187.90	$187.90
Purchase #7	$205.60	5.491%	$216.8895	$216.89	$216.90	$216.90
7 purchase totals =	$884.27		$954.5668	$954.57	$954.60	$954.60