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 $188.39   6.836%   $201.2683   $201.27   $201.25   $201.30  
  Purchase #2 $230.40   10.541%   $254.6865   $254.69   $254.70   $254.70  
  Purchase #3 $153.88   7.840%   $165.9442   $165.94   $165.95   $165.90  
  Purchase #4 $141.35   12.186%   $158.5749   $158.57   $158.55   $158.60  
  Purchase #5 $16.35   13.168%   $18.503   $18.50   $18.50   $18.50  
  Purchase #6 $130.86   4.112%   $136.241   $136.24   $136.25   $136.20  
  Purchase #7 $55.95   11.716%   $62.5051   $62.51   $62.50   $62.50  
  7 purchase totals = $917.18       $997.7230   $997.72   $997.70   $997.70