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 $74.57   13.648%   $84.7473   $84.75   $84.75   $84.70  
  Purchase #2 $247.55   12.444%   $278.3551   $278.36   $278.35   $278.40  
  Purchase #3 $103.83   5.707%   $109.7556   $109.76   $109.75   $109.80  
  Purchase #4 $36.94   4.345%   $38.545   $38.55   $38.55   $38.50  
  Purchase #5 $234.72   11.767%   $262.3395   $262.34   $262.35   $262.30  
  Purchase #6 $157.37   4.269%   $164.0881   $164.09   $164.10   $164.10  
  Purchase #7 $23.87   10.159%   $26.295   $26.30   $26.30   $26.30  
  7 purchase totals = $878.85       $964.1256   $964.15   $964.15   $964.10