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	$46.90	10.594%	$51.8686	$51.87	$51.85	$51.90
Purchase #2	$14.78	4.795%	$15.4887	$15.49	$15.50	$15.50
Purchase #3	$14.30	8.598%	$15.5295	$15.53	$15.55	$15.50
Purchase #4	$37.74	13.741%	$42.9259	$42.93	$42.95	$42.90
Purchase #5	$100.78	3.431%	$104.2378	$104.24	$104.25	$104.20
Purchase #6	$51.27	6.128%	$54.4118	$54.41	$54.40	$54.40
Purchase #7	$249.69	9.342%	$273.016	$273.02	$273.00	$273.00
7 purchase totals =	$515.46		$557.4783	$557.49	$557.50	$557.40