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	$48.35	13.504%	$54.8792	$54.88	$54.90	$54.90
Purchase #2	$234.25	6.503%	$249.4833	$249.48	$249.50	$249.50
Purchase #3	$155.99	5.295%	$164.2497	$164.25	$164.25	$164.20
Purchase #4	$170.82	5.195%	$179.6941	$179.69	$179.70	$179.70
Purchase #5	$87.47	4.853%	$91.7149	$91.71	$91.70	$91.70
Purchase #6	$73.64	12.667%	$82.968	$82.97	$82.95	$83.00
Purchase #7	$79.89	12.523%	$89.8946	$89.89	$89.90	$89.90
7 purchase totals =	$850.41		$912.8838	$912.87	$912.90	$912.90