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 $245.62   10.657%   $271.7957   $271.80   $271.80   $271.80  
  Purchase #2 $125.65   11.839%   $140.5257   $140.53   $140.55   $140.50  
  Purchase #3 $26.96   8.474%   $29.2446   $29.24   $29.25   $29.20  
  Purchase #4 $51.39   6.372%   $54.6646   $54.66   $54.65   $54.70  
  Purchase #5 $70.97   7.379%   $76.2069   $76.21   $76.20   $76.20  
  Purchase #6 $36.29   11.151%   $40.3367   $40.34   $40.35   $40.30  
  Purchase #7 $103.73   10.595%   $114.7202   $114.72   $114.70   $114.70  
  7 purchase totals = $660.61       $727.4944   $727.50   $727.50   $727.40