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 $241.98   4.553%   $252.9973   $253.00   $253.00   $253.00  
  Purchase #2 $53.46   3.566%   $55.3664   $55.37   $55.35   $55.40  
  Purchase #3 $247.85   5.617%   $261.7717   $261.77   $261.75   $261.80  
  Purchase #4 $156.63   5.355%   $165.0175   $165.02   $165.00   $165.00  
  Purchase #5 $120.76   5.649%   $127.5817   $127.58   $127.60   $127.60  
  Purchase #6 $55.65   7.514%   $59.8315   $59.83   $59.85   $59.80  
  Purchase #7 $243.73   4.548%   $254.8148   $254.81   $254.80   $254.80  
  7 purchase totals = $1,120.06       $1,177.3809   $1,177.38   $1,177.35   $1,177.40