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 $56.73   12.688%   $63.9279   $63.93   $63.95   $63.90  
  Purchase #2 $134.70   3.457%   $139.3566   $139.36   $139.35   $139.40  
  Purchase #3 $138.36   4.732%   $144.9072   $144.91   $144.90   $144.90  
  Purchase #4 $179.68   7.193%   $192.6044   $192.60   $192.60   $192.60  
  Purchase #5 $154.27   13.420%   $174.973   $174.97   $174.95   $175.00  
  Purchase #6 $248.26   7.498%   $266.8745   $266.87   $266.85   $266.90  
  Purchase #7 $48.88   10.264%   $53.897   $53.90   $53.90   $53.90  
  7 purchase totals = $960.88       $1,036.5406   $1,036.54   $1,036.50   $1,036.60