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 $52.63   9.691%   $57.7304   $57.73   $57.75   $57.70  
  Purchase #2 $85.86   3.230%   $88.6333   $88.63   $88.65   $88.60  
  Purchase #3 $45.71   11.189%   $50.8245   $50.82   $50.80   $50.80  
  Purchase #4 $77.39   13.114%   $87.5389   $87.54   $87.55   $87.50  
  Purchase #5 $249.62   5.753%   $263.9806   $263.98   $264.00   $264.00  
  Purchase #6 $221.73   5.644%   $234.2444   $234.24   $234.25   $234.20  
  Purchase #7 $130.75   4.798%   $137.0234   $137.02   $137.00   $137.00  
  7 purchase totals = $863.69       $919.9755   $919.96   $920.00   $919.80