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 $197.25   13.465%   $223.8097   $223.81   $223.80   $223.80  
  Purchase #2 $52.73   5.666%   $55.7177   $55.72   $55.70   $55.70  
  Purchase #3 $22.65   7.116%   $24.2618   $24.26   $24.25   $24.30  
  Purchase #4 $72.40   5.847%   $76.6332   $76.63   $76.65   $76.60  
  Purchase #5 $244.58   8.238%   $264.7285   $264.73   $264.75   $264.70  
  Purchase #6 $138.89   5.615%   $146.6887   $146.69   $146.70   $146.70  
  Purchase #7 $208.56   6.777%   $222.6941   $222.69   $222.70   $222.70  
  7 purchase totals = $937.06       $1,014.5337   $1,014.53   $1,014.55   $1,014.50