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	$78.61	10.502%	$86.8656	$86.87	$86.85	$86.90
Purchase #2	$92.47	6.284%	$98.2808	$98.28	$98.30	$98.30
Purchase #3	$208.33	11.848%	$233.0129	$233.01	$233.00	$233.00
Purchase #4	$34.87	6.203%	$37.033	$37.03	$37.05	$37.00
Purchase #5	$36.55	8.453%	$39.6396	$39.64	$39.65	$39.60
Purchase #6	$21.60	13.707%	$24.5607	$24.56	$24.55	$24.60
Purchase #7	$35.78	10.256%	$39.4496	$39.45	$39.45	$39.40
7 purchase totals =	$508.21		$558.8422	$558.84	$558.85	$558.80