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	$24.40	10.208%	$26.8908	$26.89	$26.90	$26.90
Purchase #2	$52.67	13.431%	$59.7441	$59.74	$59.75	$59.70
Purchase #3	$217.55	9.832%	$238.9395	$238.94	$238.95	$238.90
Purchase #4	$21.69	11.698%	$24.2273	$24.23	$24.25	$24.20
Purchase #5	$41.37	12.537%	$46.5566	$46.56	$46.55	$46.60
Purchase #6	$216.62	13.503%	$245.8702	$245.87	$245.85	$245.90
Purchase #7	$211.86	5.569%	$223.6585	$223.66	$223.65	$223.70
7 purchase totals =	$786.16		$865.8870	$865.89	$865.90	$865.90