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	$78.28	10.863%	$86.7836	$86.78	$86.80	$86.80
Purchase #2	$81.85	8.147%	$88.5183	$88.52	$88.50	$88.50
Purchase #3	$89.37	12.335%	$100.3938	$100.39	$100.40	$100.40
Purchase #4	$31.53	10.597%	$34.8712	$34.87	$34.85	$34.90
Purchase #5	$195.30	6.689%	$208.3636	$208.36	$208.35	$208.40
Purchase #6	$68.41	6.818%	$73.0742	$73.07	$73.05	$73.10
Purchase #7	$155.86	5.761%	$164.8391	$164.84	$164.85	$164.80
7 purchase totals =	$700.60		$756.8438	$756.83	$756.80	$756.90