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	$230.28	11.551%	$256.8796	$256.88	$256.90	$256.90
Purchase #2	$132.67	5.227%	$139.6047	$139.60	$139.60	$139.60
Purchase #3	$38.26	6.556%	$40.7683	$40.77	$40.75	$40.80
Purchase #4	$53.42	12.203%	$59.9388	$59.94	$59.95	$59.90
Purchase #5	$246.48	10.290%	$271.8428	$271.84	$271.85	$271.80
Purchase #6	$39.59	8.548%	$42.9742	$42.97	$42.95	$43.00
Purchase #7	$86.80	9.655%	$95.1805	$95.18	$95.20	$95.20
7 purchase totals =	$827.50		$907.1889	$907.18	$907.20	$907.20