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	$172.76	11.606%	$192.8105	$192.81	$192.80	$192.80
Purchase #2	$100.51	10.803%	$111.3681	$111.37	$111.35	$111.40
Purchase #3	$30.91	3.340%	$31.9424	$31.94	$31.95	$31.90
Purchase #4	$107.42	5.546%	$113.3775	$113.38	$113.40	$113.40
Purchase #5	$239.48	10.445%	$264.4937	$264.49	$264.50	$264.50
Purchase #6	$56.29	13.360%	$63.8103	$63.81	$63.80	$63.80
Purchase #7	$118.33	8.453%	$128.3324	$128.33	$128.35	$128.30
7 purchase totals =	$825.70		$906.1349	$906.13	$906.15	$906.10