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	$243.45	5.514%	$256.8738	$256.87	$256.85	$256.90
Purchase #2	$132.41	3.838%	$137.4919	$137.49	$137.50	$137.50
Purchase #3	$113.86	8.415%	$123.4413	$123.44	$123.45	$123.40
Purchase #4	$89.50	9.594%	$98.0866	$98.09	$98.10	$98.10
Purchase #5	$212.55	13.598%	$241.4525	$241.45	$241.45	$241.50
Purchase #6	$222.88	6.599%	$237.5879	$237.59	$237.60	$237.60
Purchase #7	$14.56	4.710%	$15.2458	$15.25	$15.25	$15.20
7 purchase totals =	$1,029.21		$1,110.1798	$1,110.18	$1,110.20	$1,110.20