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	$18.51	11.712%	$20.6779	$20.68	$20.70	$20.70
Purchase #2	$92.92	7.522%	$99.9094	$99.91	$99.90	$99.90
Purchase #3	$72.68	9.786%	$79.7925	$79.79	$79.80	$79.80
Purchase #4	$138.77	3.630%	$143.8074	$143.81	$143.80	$143.80
Purchase #5	$120.66	13.558%	$137.0191	$137.02	$137.00	$137.00
Purchase #6	$228.25	11.867%	$255.3364	$255.34	$255.35	$255.30
Purchase #7	$168.98	5.689%	$178.5933	$178.59	$178.60	$178.60
7 purchase totals =	$840.77		$915.1360	$915.14	$915.15	$915.10