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	$178.39	6.778%	$190.4813	$190.48	$190.50	$190.50
Purchase #2	$56.96	4.184%	$59.3432	$59.34	$59.35	$59.30
Purchase #3	$182.28	10.219%	$200.9072	$200.91	$200.90	$200.90
Purchase #4	$123.89	8.302%	$134.1753	$134.18	$134.20	$134.20
Purchase #5	$206.87	4.577%	$216.3384	$216.34	$216.35	$216.30
Purchase #6	$70.85	9.526%	$77.5992	$77.60	$77.60	$77.60
Purchase #7	$94.47	7.742%	$101.7839	$101.78	$101.80	$101.80
7 purchase totals =	$913.71		$980.6285	$980.63	$980.70	$980.60