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	$249.30	4.651%	$260.8949	$260.89	$260.90	$260.90
Purchase #2	$77.76	11.301%	$86.5477	$86.55	$86.55	$86.50
Purchase #3	$199.77	3.743%	$207.2474	$207.25	$207.25	$207.20
Purchase #4	$49.77	9.578%	$54.537	$54.54	$54.55	$54.50
Purchase #5	$13.63	3.389%	$14.0919	$14.09	$14.10	$14.10
Purchase #6	$121.30	9.111%	$132.3516	$132.35	$132.35	$132.40
Purchase #7	$68.90	13.718%	$78.3517	$78.35	$78.35	$78.40
7 purchase totals =	$780.43		$834.0222	$834.02	$834.05	$834.00