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 $232.38   9.176%   $253.7032   $253.70   $253.70   $253.70  
  Purchase #2 $199.27   4.863%   $208.9605   $208.96   $208.95   $209.00  
  Purchase #3 $114.44   9.774%   $125.6254   $125.63   $125.65   $125.60  
  Purchase #4 $188.67   6.826%   $201.5486   $201.55   $201.55   $201.50  
  Purchase #5 $247.47   5.414%   $260.868   $260.87   $260.85   $260.90  
  Purchase #6 $150.90   8.258%   $163.3613   $163.36   $163.35   $163.40  
  Purchase #7 $114.34   7.718%   $123.1648   $123.16   $123.15   $123.20  
  7 purchase totals = $1,247.47       $1,337.2318   $1,337.23   $1,337.20   $1,337.30