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	$192.25	8.853%	$209.2699	$209.27	$209.25	$209.30
Purchase #2	$233.92	5.538%	$246.8745	$246.87	$246.85	$246.90
Purchase #3	$49.96	11.821%	$55.8658	$55.87	$55.85	$55.90
Purchase #4	$31.44	13.223%	$35.5973	$35.60	$35.60	$35.60
Purchase #5	$68.98	3.712%	$71.5405	$71.54	$71.55	$71.50
Purchase #6	$97.71	5.363%	$102.9502	$102.95	$102.95	$103.00
Purchase #7	$44.89	12.197%	$50.3652	$50.37	$50.35	$50.40
7 purchase totals =	$719.15		$772.4634	$772.47	$772.40	$772.60