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	$39.93	6.712%	$42.6101	$42.61	$42.60	$42.60
Purchase #2	$93.55	7.557%	$100.6196	$100.62	$100.60	$100.60
Purchase #3	$149.77	9.827%	$164.4879	$164.49	$164.50	$164.50
Purchase #4	$210.71	7.667%	$226.8651	$226.87	$226.85	$226.90
Purchase #5	$54.60	3.618%	$56.5754	$56.58	$56.60	$56.60
Purchase #6	$213.53	12.563%	$240.3558	$240.36	$240.35	$240.40
Purchase #7	$33.34	3.408%	$34.4762	$34.48	$34.50	$34.50
7 purchase totals =	$795.43		$865.9901	$866.01	$866.00	$866.10