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	$61.58	8.534%	$66.8352	$66.84	$66.85	$66.80
Purchase #2	$35.69	13.154%	$40.3847	$40.38	$40.40	$40.40
Purchase #3	$108.73	9.249%	$118.7864	$118.79	$118.80	$118.80
Purchase #4	$158.78	5.833%	$168.0416	$168.04	$168.05	$168.00
Purchase #5	$236.84	10.155%	$260.8911	$260.89	$260.90	$260.90
Purchase #6	$66.62	9.457%	$72.9203	$72.92	$72.90	$72.90
Purchase #7	$86.65	13.857%	$98.6571	$98.66	$98.65	$98.70
7 purchase totals =	$754.89		$826.5164	$826.52	$826.55	$826.50