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	$28.79	9.403%	$31.4971	$31.50	$31.50	$31.50
Purchase #2	$30.96	8.225%	$33.5065	$33.51	$33.50	$33.50
Purchase #3	$216.78	13.692%	$246.4615	$246.46	$246.45	$246.50
Purchase #4	$234.51	3.518%	$242.7601	$242.76	$242.75	$242.80
Purchase #5	$113.59	4.629%	$118.8481	$118.85	$118.85	$118.80
Purchase #6	$173.95	13.204%	$196.9184	$196.92	$196.90	$196.90
Purchase #7	$93.86	3.580%	$97.2202	$97.22	$97.20	$97.20
7 purchase totals =	$892.44		$967.2119	$967.22	$967.15	$967.20