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 $205.58   13.279%   $232.879   $232.88   $232.90   $232.90  
  Purchase #2 $163.49   4.746%   $171.2492   $171.25   $171.25   $171.20  
  Purchase #3 $242.33   7.648%   $260.8634   $260.86   $260.85   $260.90  
  Purchase #4 $187.56   7.553%   $201.7264   $201.73   $201.75   $201.70  
  Purchase #5 $105.92   12.854%   $119.535   $119.54   $119.55   $119.50  
  Purchase #6 $233.25   8.310%   $252.6331   $252.63   $252.65   $252.60  
  Purchase #7 $22.64   13.710%   $25.7439   $25.74   $25.75   $25.70  
  7 purchase totals = $1,160.77       $1,264.6300   $1,264.63   $1,264.70   $1,264.50