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	$81.40	10.783%	$90.1774	$90.18	$90.20	$90.20
Purchase #2	$234.73	5.687%	$248.0791	$248.08	$248.10	$248.10
Purchase #3	$62.94	9.665%	$69.0232	$69.02	$69.00	$69.00
Purchase #4	$77.27	6.730%	$82.4703	$82.47	$82.45	$82.50
Purchase #5	$43.45	13.563%	$49.3431	$49.34	$49.35	$49.30
Purchase #6	$42.83	7.177%	$45.9039	$45.90	$45.90	$45.90
Purchase #7	$73.31	5.696%	$77.4857	$77.49	$77.50	$77.50
7 purchase totals =	$615.93		$662.4827	$662.48	$662.50	$662.50