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	$135.93	4.390%	$141.8973	$141.90	$141.90	$141.90
Purchase #2	$150.35	9.290%	$164.3175	$164.32	$164.30	$164.30
Purchase #3	$10.44	9.621%	$11.4444	$11.44	$11.45	$11.40
Purchase #4	$176.83	13.617%	$200.9089	$200.91	$200.90	$200.90
Purchase #5	$39.37	5.139%	$41.3932	$41.39	$41.40	$41.40
Purchase #6	$213.46	4.207%	$222.4403	$222.44	$222.45	$222.40
Purchase #7	$70.85	10.207%	$78.0817	$78.08	$78.10	$78.10
7 purchase totals =	$797.23		$860.4833	$860.48	$860.50	$860.40