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	$32.29	13.535%	$36.6605	$36.66	$36.65	$36.70
Purchase #2	$88.87	4.455%	$92.8292	$92.83	$92.85	$92.80
Purchase #3	$137.63	3.715%	$142.743	$142.74	$142.75	$142.70
Purchase #4	$241.46	10.412%	$266.6008	$266.60	$266.60	$266.60
Purchase #5	$215.80	13.111%	$244.0935	$244.09	$244.10	$244.10
Purchase #6	$17.70	5.776%	$18.7224	$18.72	$18.70	$18.70
Purchase #7	$241.83	13.575%	$274.6584	$274.66	$274.65	$274.70
7 purchase totals =	$975.58		$1,076.3078	$1,076.30	$1,076.30	$1,076.30