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	$81.31	12.490%	$91.4656	$91.47	$91.45	$91.50
Purchase #2	$151.28	10.592%	$167.3036	$167.30	$167.30	$167.30
Purchase #3	$135.47	13.652%	$153.9644	$153.96	$153.95	$154.00
Purchase #4	$16.59	11.655%	$18.5236	$18.52	$18.50	$18.50
Purchase #5	$94.68	5.705%	$100.0815	$100.08	$100.10	$100.10
Purchase #6	$23.45	7.860%	$25.2932	$25.29	$25.30	$25.30
Purchase #7	$44.96	10.842%	$49.8346	$49.83	$49.85	$49.80
7 purchase totals =	$547.74		$606.4665	$606.45	$606.45	$606.50