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	$123.29	13.237%	$139.6099	$139.61	$139.60	$139.60
Purchase #2	$29.32	8.726%	$31.8785	$31.88	$31.90	$31.90
Purchase #3	$234.61	11.526%	$261.6511	$261.65	$261.65	$261.70
Purchase #4	$165.90	6.645%	$176.9241	$176.92	$176.90	$176.90
Purchase #5	$90.70	5.676%	$95.8481	$95.85	$95.85	$95.80
Purchase #6	$190.45	3.190%	$196.5254	$196.53	$196.55	$196.50
Purchase #7	$65.56	4.656%	$68.6125	$68.61	$68.60	$68.60
7 purchase totals =	$899.83		$971.0496	$971.05	$971.05	$971.00