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	$10.32	9.546%	$11.3051	$11.31	$11.30	$11.30
Purchase #2	$93.94	7.469%	$100.9564	$100.96	$100.95	$101.00
Purchase #3	$182.31	7.803%	$196.5356	$196.54	$196.55	$196.50
Purchase #4	$227.31	5.376%	$239.5302	$239.53	$239.55	$239.50
Purchase #5	$38.48	7.509%	$41.3695	$41.37	$41.35	$41.40
Purchase #6	$146.67	4.325%	$153.0135	$153.01	$153.00	$153.00
Purchase #7	$84.42	5.165%	$88.7803	$88.78	$88.80	$88.80
7 purchase totals =	$783.45		$831.4906	$831.50	$831.50	$831.50