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	$85.44	5.640%	$90.2588	$90.26	$90.25	$90.30
Purchase #2	$51.46	6.595%	$54.8538	$54.85	$54.85	$54.90
Purchase #3	$177.46	10.704%	$196.4553	$196.46	$196.45	$196.50
Purchase #4	$85.43	7.781%	$92.0773	$92.08	$92.10	$92.10
Purchase #5	$64.37	3.301%	$66.4949	$66.49	$66.50	$66.50
Purchase #6	$73.57	6.796%	$78.5698	$78.57	$78.55	$78.60
Purchase #7	$10.80	6.204%	$11.47	$11.47	$11.45	$11.50
7 purchase totals =	$548.53		$590.1799	$590.18	$590.15	$590.40