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	$87.35	3.143%	$90.0954	$90.10	$90.10	$90.10
Purchase #2	$100.72	11.656%	$112.4599	$112.46	$112.45	$112.50
Purchase #3	$192.97	4.693%	$202.0261	$202.03	$202.05	$202.00
Purchase #4	$86.54	9.482%	$94.7457	$94.75	$94.75	$94.70
Purchase #5	$208.66	3.462%	$215.8838	$215.88	$215.90	$215.90
Purchase #6	$193.41	11.415%	$215.4878	$215.49	$215.50	$215.50
Purchase #7	$213.70	12.694%	$240.8271	$240.83	$240.85	$240.80
7 purchase totals =	$1,083.35		$1,171.5258	$1,171.54	$1,171.60	$1,171.50