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 $51.47   13.417%   $58.3757   $58.38   $58.40   $58.40  
  Purchase #2 $157.63   12.106%   $176.7127   $176.71   $176.70   $176.70  
  Purchase #3 $203.32   5.167%   $213.8255   $213.83   $213.85   $213.80  
  Purchase #4 $168.30   3.504%   $174.1972   $174.20   $174.20   $174.20  
  Purchase #5 $207.31   10.863%   $229.8301   $229.83   $229.85   $229.80  
  Purchase #6 $67.98   7.641%   $73.1744   $73.17   $73.15   $73.20  
  Purchase #7 $236.94   5.262%   $249.4078   $249.41   $249.40   $249.40  
  7 purchase totals = $1,092.95       $1,175.5234   $1,175.53   $1,175.55   $1,175.50