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	$221.54	8.260%	$239.8392	$239.84	$239.85	$239.80
Purchase #2	$75.72	12.526%	$85.2047	$85.20	$85.20	$85.20
Purchase #3	$77.41	13.414%	$87.7938	$87.79	$87.80	$87.80
Purchase #4	$40.98	10.189%	$45.1555	$45.16	$45.15	$45.20
Purchase #5	$116.71	5.478%	$123.1034	$123.10	$123.10	$123.10
Purchase #6	$9.80	3.729%	$10.1654	$10.17	$10.15	$10.20
Purchase #7	$183.34	4.116%	$190.8863	$190.89	$190.90	$190.90
7 purchase totals =	$725.50		$782.1483	$782.15	$782.15	$782.20