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 $111.46   10.553%   $123.2224   $123.22   $123.20   $123.20  
  Purchase #2 $98.98   5.267%   $104.1933   $104.19   $104.20   $104.20  
  Purchase #3 $95.53   13.272%   $108.2087   $108.21   $108.20   $108.20  
  Purchase #4 $89.49   10.276%   $98.686   $98.69   $98.70   $98.70  
  Purchase #5 $248.92   5.115%   $261.6523   $261.65   $261.65   $261.70  
  Purchase #6 $248.67   12.326%   $279.3211   $279.32   $279.30   $279.30  
  Purchase #7 $169.33   3.471%   $175.2074   $175.21   $175.20   $175.20  
  7 purchase totals = $1,062.38       $1,150.4912   $1,150.49   $1,150.45   $1,150.50