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 $82.85   10.225%   $91.3214   $91.32   $91.30   $91.30  
  Purchase #2 $99.69   13.204%   $112.8531   $112.85   $112.85   $112.90  
  Purchase #3 $72.92   5.208%   $76.7177   $76.72   $76.70   $76.70  
  Purchase #4 $235.31   8.653%   $255.6714   $255.67   $255.65   $255.70  
  Purchase #5 $121.29   10.869%   $134.473   $134.47   $134.45   $134.50  
  Purchase #6 $163.48   11.354%   $182.0415   $182.04   $182.05   $182.00  
  Purchase #7 $135.63   13.222%   $153.563   $153.56   $153.55   $153.60  
  7 purchase totals = $911.17       $1,006.6411   $1,006.63   $1,006.55   $1,006.70