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 $64.95   13.253%   $73.5578   $73.56   $73.55   $73.60  
  Purchase #2 $249.72   11.671%   $278.8648   $278.86   $278.85   $278.90  
  Purchase #3 $57.76   12.635%   $65.058   $65.06   $65.05   $65.10  
  Purchase #4 $51.62   7.235%   $55.3547   $55.35   $55.35   $55.40  
  Purchase #5 $22.86   4.759%   $23.9479   $23.95   $23.95   $23.90  
  Purchase #6 $40.45   10.418%   $44.6641   $44.66   $44.65   $44.70  
  Purchase #7 $161.56   7.115%   $173.055   $173.06   $173.05   $173.10  
  7 purchase totals = $648.92       $714.5023   $714.50   $714.45   $714.70