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	$163.56	5.547%	$172.6327	$172.63	$172.65	$172.60
Purchase #2	$46.72	10.789%	$51.7606	$51.76	$51.75	$51.80
Purchase #3	$187.95	13.725%	$213.7461	$213.75	$213.75	$213.70
Purchase #4	$113.78	12.208%	$127.6703	$127.67	$127.65	$127.70
Purchase #5	$76.80	11.740%	$85.8163	$85.82	$85.80	$85.80
Purchase #6	$91.85	8.806%	$99.9383	$99.94	$99.95	$99.90
Purchase #7	$76.92	4.280%	$80.2122	$80.21	$80.20	$80.20
7 purchase totals =	$757.58		$831.7765	$831.78	$831.75	$831.70