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	$45.98	12.761%	$51.8475	$51.85	$51.85	$51.80
Purchase #2	$131.67	9.368%	$144.0048	$144.00	$144.00	$144.00
Purchase #3	$247.99	9.835%	$272.3798	$272.38	$272.40	$272.40
Purchase #4	$32.46	4.579%	$33.9463	$33.95	$33.95	$33.90
Purchase #5	$159.44	7.807%	$171.8875	$171.89	$171.90	$171.90
Purchase #6	$94.57	8.335%	$102.4524	$102.45	$102.45	$102.50
Purchase #7	$213.83	3.314%	$220.9163	$220.92	$220.90	$220.90
7 purchase totals =	$925.94		$997.4346	$997.44	$997.45	$997.40