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	$51.29	9.815%	$56.3241	$56.32	$56.30	$56.30
Purchase #2	$34.52	11.807%	$38.5958	$38.60	$38.60	$38.60
Purchase #3	$103.66	9.573%	$113.5834	$113.58	$113.60	$113.60
Purchase #4	$199.71	11.215%	$222.1075	$222.11	$222.10	$222.10
Purchase #5	$136.50	13.240%	$154.5726	$154.57	$154.55	$154.60
Purchase #6	$36.74	7.423%	$39.4672	$39.47	$39.45	$39.50
Purchase #7	$82.92	5.274%	$87.2932	$87.29	$87.30	$87.30
7 purchase totals =	$645.34		$711.9438	$711.94	$711.90	$712.00