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	$121.90	7.467%	$131.0023	$131.00	$131.00	$131.00
Purchase #2	$152.86	3.563%	$158.3064	$158.31	$158.30	$158.30
Purchase #3	$112.34	7.274%	$120.5116	$120.51	$120.50	$120.50
Purchase #4	$138.66	12.691%	$156.2573	$156.26	$156.25	$156.30
Purchase #5	$244.27	7.600%	$262.8345	$262.83	$262.85	$262.80
Purchase #6	$5.27	10.573%	$5.8272	$5.83	$5.85	$5.80
Purchase #7	$81.51	13.204%	$92.2726	$92.27	$92.25	$92.30
7 purchase totals =	$856.81		$927.0119	$927.01	$927.00	$927.00