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 $168.55   10.593%   $186.4045   $186.40   $186.40   $186.40  
  Purchase #2 $168.74   6.187%   $179.1799   $179.18   $179.20   $179.20  
  Purchase #3 $64.94   12.373%   $72.975   $72.98   $73.00   $73.00  
  Purchase #4 $101.27   5.287%   $106.6241   $106.62   $106.60   $106.60  
  Purchase #5 $94.36   7.429%   $101.37   $101.37   $101.35   $101.40  
  Purchase #6 $196.63   12.766%   $221.7318   $221.73   $221.75   $221.70  
  Purchase #7 $98.61   7.189%   $105.6991   $105.70   $105.70   $105.70  
  7 purchase totals = $893.10       $973.9844   $973.98   $974.00   $974.00