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	$95.54	4.738%	$100.0667	$100.07	$100.05	$100.10
Purchase #2	$64.30	13.478%	$72.9664	$72.97	$72.95	$73.00
Purchase #3	$94.85	5.343%	$99.9178	$99.92	$99.90	$99.90
Purchase #4	$73.57	9.828%	$80.8005	$80.80	$80.80	$80.80
Purchase #5	$214.38	12.872%	$241.975	$241.98	$242.00	$242.00
Purchase #6	$212.84	3.470%	$220.2255	$220.23	$220.25	$220.20
Purchase #7	$116.75	9.215%	$127.5085	$127.51	$127.50	$127.50
7 purchase totals =	$872.23		$943.4604	$943.48	$943.45	$943.50