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	$239.65	11.562%	$267.3583	$267.36	$267.35	$267.40
Purchase #2	$197.98	12.873%	$223.466	$223.47	$223.45	$223.50
Purchase #3	$66.69	8.138%	$72.1172	$72.12	$72.10	$72.10
Purchase #4	$33.85	4.747%	$35.4569	$35.46	$35.45	$35.50
Purchase #5	$87.55	9.246%	$95.6449	$95.64	$95.65	$95.60
Purchase #6	$127.80	3.568%	$132.3599	$132.36	$132.35	$132.40
Purchase #7	$114.78	4.155%	$119.5491	$119.55	$119.55	$119.50
7 purchase totals =	$868.30		$945.9523	$945.96	$945.90	$946.00