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	$240.77	10.857%	$266.9104	$266.91	$266.90	$266.90
Purchase #2	$36.51	3.827%	$37.9072	$37.91	$37.90	$37.90
Purchase #3	$224.90	6.495%	$239.5073	$239.51	$239.50	$239.50
Purchase #4	$224.91	13.489%	$255.2481	$255.25	$255.25	$255.20
Purchase #5	$136.96	8.686%	$148.8563	$148.86	$148.85	$148.90
Purchase #6	$145.88	10.818%	$161.6613	$161.66	$161.65	$161.70
Purchase #7	$38.34	5.742%	$40.5415	$40.54	$40.55	$40.50
7 purchase totals =	$1,048.27		$1,150.6321	$1,150.64	$1,150.60	$1,150.60