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 $55.86   12.695%   $62.9514   $62.95   $62.95   $63.00  
  Purchase #2 $182.37   11.611%   $203.545   $203.55   $203.55   $203.50  
  Purchase #3 $174.86   9.210%   $190.9646   $190.96   $190.95   $191.00  
  Purchase #4 $232.85   12.371%   $261.6559   $261.66   $261.65   $261.70  
  Purchase #5 $234.90   10.379%   $259.2803   $259.28   $259.30   $259.30  
  Purchase #6 $41.39   4.543%   $43.2703   $43.27   $43.25   $43.30  
  Purchase #7 $215.54   5.261%   $226.8796   $226.88   $226.90   $226.90  
  7 purchase totals = $1,137.77       $1,248.5471   $1,248.55   $1,248.55   $1,248.70