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 $124.59   5.710%   $131.7041   $131.70   $131.70   $131.70  
  Purchase #2 $201.62   12.420%   $226.6612   $226.66   $226.65   $226.70  
  Purchase #3 $187.65   11.359%   $208.9652   $208.97   $208.95   $209.00  
  Purchase #4 $246.27   13.721%   $280.0607   $280.06   $280.05   $280.10  
  Purchase #5 $127.74   7.550%   $137.3844   $137.38   $137.40   $137.40  
  Purchase #6 $114.42   4.198%   $119.2234   $119.22   $119.20   $119.20  
  Purchase #7 $26.26   7.604%   $28.2568   $28.26   $28.25   $28.30  
  7 purchase totals = $1,028.55       $1,132.2558   $1,132.25   $1,132.20   $1,132.40