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	$187.29	12.476%	$210.6563	$210.66	$210.65	$210.70
Purchase #2	$87.85	13.841%	$100.0093	$100.01	$100.00	$100.00
Purchase #3	$21.93	9.752%	$24.0686	$24.07	$24.05	$24.10
Purchase #4	$196.66	8.602%	$213.5767	$213.58	$213.60	$213.60
Purchase #5	$202.63	6.601%	$216.0056	$216.01	$216.00	$216.00
Purchase #6	$153.89	9.581%	$168.6342	$168.63	$168.65	$168.60
Purchase #7	$56.38	5.501%	$59.4815	$59.48	$59.50	$59.50
7 purchase totals =	$906.63		$992.4322	$992.44	$992.45	$992.50