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 $112.82   12.695%   $127.1425   $127.14   $127.15   $127.10  
  Purchase #2 $210.84   11.312%   $234.6902   $234.69   $234.70   $234.70  
  Purchase #3 $105.69   12.781%   $119.1982   $119.20   $119.20   $119.20  
  Purchase #4 $249.71   5.744%   $264.0533   $264.05   $264.05   $264.10  
  Purchase #5 $130.98   9.829%   $143.854   $143.85   $143.85   $143.90  
  Purchase #6 $73.73   12.670%   $83.0716   $83.07   $83.05   $83.10  
  Purchase #7 $71.92   13.648%   $81.7356   $81.74   $81.75   $81.70  
  7 purchase totals = $955.69       $1,053.7454   $1,053.74   $1,053.75   $1,053.80