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	$38.59	3.363%	$39.8878	$39.89	$39.90	$39.90
Purchase #2	$68.32	6.559%	$72.8011	$72.80	$72.80	$72.80
Purchase #3	$201.38	8.526%	$218.5497	$218.55	$218.55	$218.50
Purchase #4	$138.79	10.812%	$153.796	$153.80	$153.80	$153.80
Purchase #5	$223.54	9.307%	$244.3449	$244.34	$244.35	$244.30
Purchase #6	$36.83	13.643%	$41.8547	$41.85	$41.85	$41.90
Purchase #7	$78.65	13.411%	$89.1978	$89.20	$89.20	$89.20
7 purchase totals =	$786.10		$860.4320	$860.43	$860.45	$860.40