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 $91.70   13.256%   $103.8558   $103.86   $103.85   $103.90  
  Purchase #2 $107.37   11.424%   $119.6359   $119.64   $119.65   $119.60  
  Purchase #3 $246.77   11.524%   $275.2078   $275.21   $275.20   $275.20  
  Purchase #4 $125.49   12.470%   $141.1386   $141.14   $141.15   $141.10  
  Purchase #5 $164.66   6.602%   $175.5309   $175.53   $175.55   $175.50  
  Purchase #6 $26.61   7.119%   $28.5044   $28.50   $28.50   $28.50  
  Purchase #7 $119.73   8.338%   $129.7131   $129.71   $129.70   $129.70  
  7 purchase totals = $882.33       $973.5865   $973.59   $973.60   $973.50