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	$125.27	13.103%	$141.6841	$141.68	$141.70	$141.70
Purchase #2	$75.50	10.343%	$83.309	$83.31	$83.30	$83.30
Purchase #3	$148.49	5.619%	$156.8337	$156.83	$156.85	$156.80
Purchase #4	$225.90	10.647%	$249.9516	$249.95	$249.95	$250.00
Purchase #5	$53.38	4.241%	$55.6438	$55.64	$55.65	$55.60
Purchase #6	$132.74	3.454%	$137.3248	$137.32	$137.30	$137.30
Purchase #7	$42.96	13.806%	$48.8911	$48.89	$48.90	$48.90
7 purchase totals =	$804.24		$873.6381	$873.62	$873.65	$873.60