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	$95.96	13.442%	$108.8589	$108.86	$108.85	$108.90
Purchase #2	$18.73	12.230%	$21.0207	$21.02	$21.00	$21.00
Purchase #3	$20.34	7.626%	$21.8911	$21.89	$21.90	$21.90
Purchase #4	$32.29	4.339%	$33.6911	$33.69	$33.70	$33.70
Purchase #5	$166.60	6.135%	$176.8209	$176.82	$176.80	$176.80
Purchase #6	$127.38	7.415%	$136.8252	$136.83	$136.85	$136.80
Purchase #7	$15.80	9.838%	$17.3544	$17.35	$17.35	$17.40
7 purchase totals =	$477.10		$516.4623	$516.46	$516.45	$516.50