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	$85.33	10.632%	$94.4023	$94.40	$94.40	$94.40
Purchase #2	$91.54	12.327%	$102.8241	$102.82	$102.80	$102.80
Purchase #3	$132.42	5.322%	$139.4674	$139.47	$139.45	$139.50
Purchase #4	$104.39	11.487%	$116.3813	$116.38	$116.40	$116.40
Purchase #5	$236.87	7.645%	$254.9787	$254.98	$255.00	$255.00
Purchase #6	$140.82	4.244%	$146.7964	$146.80	$146.80	$146.80
Purchase #7	$123.83	5.714%	$130.9056	$130.91	$130.90	$130.90
7 purchase totals =	$915.20		$985.7558	$985.76	$985.75	$985.80