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	$168.42	12.767%	$189.9222	$189.92	$189.90	$189.90
Purchase #2	$244.76	11.218%	$272.2172	$272.22	$272.20	$272.20
Purchase #3	$118.69	8.114%	$128.3205	$128.32	$128.30	$128.30
Purchase #4	$78.71	5.797%	$83.2728	$83.27	$83.25	$83.30
Purchase #5	$5.47	3.126%	$5.641	$5.64	$5.65	$5.60
Purchase #6	$169.25	12.595%	$190.567	$190.57	$190.55	$190.60
Purchase #7	$113.87	12.141%	$127.695	$127.70	$127.70	$127.70
7 purchase totals =	$899.17		$997.6357	$997.64	$997.55	$997.60