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	$155.43	11.235%	$172.8926	$172.89	$172.90	$172.90
Purchase #2	$172.77	5.525%	$182.3155	$182.32	$182.30	$182.30
Purchase #3	$78.43	5.158%	$82.4754	$82.48	$82.50	$82.50
Purchase #4	$205.86	4.854%	$215.8524	$215.85	$215.85	$215.90
Purchase #5	$97.81	9.189%	$106.7978	$106.80	$106.80	$106.80
Purchase #6	$129.69	11.454%	$144.5447	$144.54	$144.55	$144.50
Purchase #7	$12.46	4.109%	$12.972	$12.97	$12.95	$13.00
7 purchase totals =	$852.45		$917.8504	$917.85	$917.85	$917.90