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	$59.92	10.770%	$66.3734	$66.37	$66.35	$66.40
Purchase #2	$21.90	12.173%	$24.5659	$24.57	$24.55	$24.60
Purchase #3	$147.85	10.156%	$162.8656	$162.87	$162.85	$162.90
Purchase #4	$92.99	13.401%	$105.4516	$105.45	$105.45	$105.50
Purchase #5	$43.64	9.210%	$47.6592	$47.66	$47.65	$47.70
Purchase #6	$13.83	4.529%	$14.4564	$14.46	$14.45	$14.50
Purchase #7	$113.43	4.217%	$118.2133	$118.21	$118.20	$118.20
7 purchase totals =	$493.56		$539.5854	$539.59	$539.50	$539.80