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	$131.88	6.550%	$140.5181	$140.52	$140.50	$140.50
Purchase #2	$28.73	12.388%	$32.2891	$32.29	$32.30	$32.30
Purchase #3	$164.72	7.247%	$176.6573	$176.66	$176.65	$176.70
Purchase #4	$208.61	3.258%	$215.4065	$215.41	$215.40	$215.40
Purchase #5	$101.86	11.404%	$113.4761	$113.48	$113.50	$113.50
Purchase #6	$151.99	11.184%	$168.9886	$168.99	$169.00	$169.00
Purchase #7	$21.62	13.298%	$24.495	$24.50	$24.50	$24.50
7 purchase totals =	$809.41		$871.8307	$871.85	$871.85	$871.90