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	$31.80	12.323%	$35.7187	$35.72	$35.70	$35.70
Purchase #2	$82.51	9.515%	$90.3608	$90.36	$90.35	$90.40
Purchase #3	$236.87	5.559%	$250.0376	$250.04	$250.05	$250.00
Purchase #4	$202.73	5.819%	$214.5269	$214.53	$214.55	$214.50
Purchase #5	$65.38	10.716%	$72.3861	$72.39	$72.40	$72.40
Purchase #6	$124.25	10.168%	$136.8837	$136.88	$136.90	$136.90
Purchase #7	$136.95	10.756%	$151.6803	$151.68	$151.70	$151.70
7 purchase totals =	$880.49		$951.5941	$951.60	$951.65	$951.60