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 $245.85   7.809%   $265.0484   $265.05   $265.05   $265.00  
  Purchase #2 $191.61   12.235%   $215.0535   $215.05   $215.05   $215.10  
  Purchase #3 $146.74   7.169%   $157.2598   $157.26   $157.25   $157.30  
  Purchase #4 $190.66   7.354%   $204.6811   $204.68   $204.70   $204.70  
  Purchase #5 $27.74   8.490%   $30.0951   $30.10   $30.10   $30.10  
  Purchase #6 $158.55   3.565%   $164.2023   $164.20   $164.20   $164.20  
  Purchase #7 $10.98   7.474%   $11.8006   $11.80   $11.80   $11.80  
  7 purchase totals = $972.13       $1,048.1408   $1,048.14   $1,048.15   $1,048.20