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 $221.62   6.604%   $236.2558   $236.26   $236.25   $236.30  
  Purchase #2 $243.81   13.339%   $276.3318   $276.33   $276.35   $276.30  
  Purchase #3 $125.92   12.433%   $141.5756   $141.58   $141.60   $141.60  
  Purchase #4 $116.76   4.577%   $122.1041   $122.10   $122.10   $122.10  
  Purchase #5 $191.42   10.675%   $211.8541   $211.85   $211.85   $211.90  
  Purchase #6 $225.47   7.476%   $242.3261   $242.33   $242.35   $242.30  
  Purchase #7 $75.93   9.547%   $83.179   $83.18   $83.20   $83.20  
  7 purchase totals = $1,200.93       $1,313.6265   $1,313.63   $1,313.70   $1,313.70