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 $87.27   8.143%   $94.3764   $94.38   $94.40   $94.40  
  Purchase #2 $241.74   6.643%   $257.7988   $257.80   $257.80   $257.80  
  Purchase #3 $66.39   12.821%   $74.9019   $74.90   $74.90   $74.90  
  Purchase #4 $190.86   4.432%   $199.3189   $199.32   $199.30   $199.30  
  Purchase #5 $179.42   9.548%   $196.551   $196.55   $196.55   $196.60  
  Purchase #6 $241.43   8.497%   $261.9443   $261.94   $261.95   $261.90  
  Purchase #7 $146.25   6.460%   $155.6978   $155.70   $155.70   $155.70  
  7 purchase totals = $1,153.36       $1,240.5891   $1,240.59   $1,240.60   $1,240.60