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 $119.66   13.811%   $136.1862   $136.19   $136.20   $136.20  
  Purchase #2 $55.27   10.735%   $61.2032   $61.20   $61.20   $61.20  
  Purchase #3 $208.30   12.198%   $233.7084   $233.71   $233.70   $233.70  
  Purchase #4 $171.65   11.702%   $191.7365   $191.74   $191.75   $191.70  
  Purchase #5 $250.97   3.695%   $260.2433   $260.24   $260.25   $260.20  
  Purchase #6 $62.40   8.463%   $67.6809   $67.68   $67.70   $67.70  
  Purchase #7 $81.63   5.299%   $85.9556   $85.96   $85.95   $86.00  
  7 purchase totals = $949.88       $1,036.7141   $1,036.72   $1,036.75   $1,036.70