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	$99.66	4.249%	$103.8946	$103.89	$103.90	$103.90
Purchase #2	$37.76	11.589%	$42.136	$42.14	$42.15	$42.10
Purchase #3	$182.51	4.443%	$190.6189	$190.62	$190.60	$190.60
Purchase #4	$220.48	5.527%	$232.6659	$232.67	$232.65	$232.70
Purchase #5	$102.84	10.742%	$113.8871	$113.89	$113.90	$113.90
Purchase #6	$225.54	11.219%	$250.8433	$250.84	$250.85	$250.80
Purchase #7	$146.29	11.545%	$163.1792	$163.18	$163.20	$163.20
7 purchase totals =	$1,015.08		$1,097.2250	$1,097.23	$1,097.25	$1,097.20