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 $47.98   12.135%   $53.8024   $53.80   $53.80   $53.80  
  Purchase #2 $236.28   10.779%   $261.7486   $261.75   $261.75   $261.70  
  Purchase #3 $36.92   12.567%   $41.5597   $41.56   $41.55   $41.60  
  Purchase #4 $181.59   6.516%   $193.4224   $193.42   $193.40   $193.40  
  Purchase #5 $199.67   13.677%   $226.9789   $226.98   $227.00   $227.00  
  Purchase #6 $63.59   10.715%   $70.4037   $70.40   $70.40   $70.40  
  Purchase #7 $148.72   4.714%   $155.7307   $155.73   $155.75   $155.70  
  7 purchase totals = $914.75       $1,003.6464   $1,003.64   $1,003.65   $1,003.60