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	$238.63	5.427%	$251.5805	$251.58	$251.60	$251.60
Purchase #2	$147.94	11.364%	$164.7519	$164.75	$164.75	$164.80
Purchase #3	$29.38	7.351%	$31.5397	$31.54	$31.55	$31.50
Purchase #4	$36.75	12.149%	$41.2148	$41.21	$41.20	$41.20
Purchase #5	$171.48	11.287%	$190.8349	$190.83	$190.85	$190.80
Purchase #6	$172.50	10.405%	$190.4486	$190.45	$190.45	$190.40
Purchase #7	$34.34	7.438%	$36.8942	$36.89	$36.90	$36.90
7 purchase totals =	$831.02		$907.2646	$907.25	$907.30	$907.20