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 $241.51   8.238%   $261.4056   $261.41   $261.40   $261.40  
  Purchase #2 $248.98   10.126%   $274.1917   $274.19   $274.20   $274.20  
  Purchase #3 $235.68   13.343%   $267.1268   $267.13   $267.15   $267.10  
  Purchase #4 $157.53   13.291%   $178.4673   $178.47   $178.45   $178.50  
  Purchase #5 $57.51   6.109%   $61.0233   $61.02   $61.00   $61.00  
  Purchase #6 $228.63   7.372%   $245.4846   $245.48   $245.50   $245.50  
  Purchase #7 $141.86   10.151%   $156.2602   $156.26   $156.25   $156.30  
  7 purchase totals = $1,311.70       $1,443.9595   $1,443.96   $1,443.95   $1,444.00