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	$208.78	12.302%	$234.4641	$234.46	$234.45	$234.50
Purchase #2	$59.79	11.778%	$66.8321	$66.83	$66.85	$66.80
Purchase #3	$74.50	12.695%	$83.9578	$83.96	$83.95	$84.00
Purchase #4	$65.79	10.211%	$72.5078	$72.51	$72.50	$72.50
Purchase #5	$22.55	10.319%	$24.8769	$24.88	$24.90	$24.90
Purchase #6	$135.50	12.670%	$152.6679	$152.67	$152.65	$152.70
Purchase #7	$245.47	11.175%	$272.9013	$272.90	$272.90	$272.90
7 purchase totals =	$812.38		$908.2079	$908.21	$908.20	$908.30