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 $212.60   9.204%   $232.1677   $232.17   $232.15   $232.20  
  Purchase #2 $228.91   12.838%   $258.2975   $258.30   $258.30   $258.30  
  Purchase #3 $71.48   9.225%   $78.074   $78.07   $78.05   $78.10  
  Purchase #4 $203.32   13.637%   $231.0467   $231.05   $231.05   $231.00  
  Purchase #5 $82.47   3.253%   $85.1527   $85.15   $85.15   $85.20  
  Purchase #6 $47.66   12.478%   $53.607   $53.61   $53.60   $53.60  
  Purchase #7 $23.33   5.871%   $24.6997   $24.70   $24.70   $24.70  
  7 purchase totals = $869.77       $963.0453   $963.05   $963.00   $963.10