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	$162.37	6.383%	$172.7341	$172.73	$172.75	$172.70
Purchase #2	$203.61	8.493%	$220.9026	$220.90	$220.90	$220.90
Purchase #3	$75.43	10.704%	$83.504	$83.50	$83.50	$83.50
Purchase #4	$71.37	12.208%	$80.0828	$80.08	$80.10	$80.10
Purchase #5	$72.61	13.303%	$82.2693	$82.27	$82.25	$82.30
Purchase #6	$54.93	11.215%	$61.0904	$61.09	$61.10	$61.10
Purchase #7	$124.75	13.314%	$141.3592	$141.36	$141.35	$141.40
7 purchase totals =	$765.07		$841.9424	$841.93	$841.95	$842.00