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 $127.59   7.570%   $137.2486   $137.25   $137.25   $137.20  
  Purchase #2 $235.68   10.158%   $259.6204   $259.62   $259.60   $259.60  
  Purchase #3 $95.77   4.341%   $99.9274   $99.93   $99.95   $99.90  
  Purchase #4 $216.80   5.154%   $227.9739   $227.97   $227.95   $228.00  
  Purchase #5 $59.46   7.677%   $64.0247   $64.02   $64.00   $64.00  
  Purchase #6 $212.54   5.361%   $223.9343   $223.93   $223.95   $223.90  
  Purchase #7 $114.61   6.681%   $122.2671   $122.27   $122.25   $122.30  
  7 purchase totals = $1,062.45       $1,134.9964   $1,134.99   $1,134.95   $1,134.90