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 $184.47   10.548%   $203.9279   $203.93   $203.95   $203.90  
  Purchase #2 $98.98   4.621%   $103.5539   $103.55   $103.55   $103.60  
  Purchase #3 $216.34   5.117%   $227.4101   $227.41   $227.40   $227.40  
  Purchase #4 $129.70   7.473%   $139.3925   $139.39   $139.40   $139.40  
  Purchase #5 $93.96   11.404%   $104.6752   $104.68   $104.70   $104.70  
  Purchase #6 $111.56   12.869%   $125.9167   $125.92   $125.90   $125.90  
  Purchase #7 $67.49   7.536%   $72.576   $72.58   $72.60   $72.60  
  7 purchase totals = $902.50       $977.4523   $977.46   $977.50   $977.50