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	$127.64	8.791%	$138.8608	$138.86	$138.85	$138.90
Purchase #2	$95.50	5.141%	$100.4097	$100.41	$100.40	$100.40
Purchase #3	$158.34	11.526%	$176.5903	$176.59	$176.60	$176.60
Purchase #4	$34.26	10.443%	$37.8378	$37.84	$37.85	$37.80
Purchase #5	$135.26	8.279%	$146.4582	$146.46	$146.45	$146.50
Purchase #6	$74.82	8.630%	$81.277	$81.28	$81.30	$81.30
Purchase #7	$38.86	5.556%	$41.0191	$41.02	$41.00	$41.00
7 purchase totals =	$664.68		$722.4529	$722.46	$722.45	$722.50