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	$188.76	10.623%	$208.812	$208.81	$208.80	$208.80
Purchase #2	$117.63	5.689%	$124.322	$124.32	$124.30	$124.30
Purchase #3	$39.50	5.343%	$41.6105	$41.61	$41.60	$41.60
Purchase #4	$59.66	11.610%	$66.5865	$66.59	$66.60	$66.60
Purchase #5	$122.30	13.620%	$138.9573	$138.96	$138.95	$139.00
Purchase #6	$27.77	13.265%	$31.4537	$31.45	$31.45	$31.50
Purchase #7	$54.77	3.769%	$56.8343	$56.83	$56.85	$56.80
7 purchase totals =	$610.39		$668.5763	$668.57	$668.55	$668.60