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 $207.80   6.620%   $221.5564   $221.56   $221.55   $221.60  
  Purchase #2 $165.28   8.361%   $179.0991   $179.10   $179.10   $179.10  
  Purchase #3 $211.51   11.698%   $236.2524   $236.25   $236.25   $236.30  
  Purchase #4 $44.65   13.387%   $50.6273   $50.63   $50.65   $50.60  
  Purchase #5 $40.39   6.669%   $43.0836   $43.08   $43.10   $43.10  
  Purchase #6 $154.32   6.232%   $163.9372   $163.94   $163.95   $163.90  
  Purchase #7 $131.73   3.766%   $136.691   $136.69   $136.70   $136.70  
  7 purchase totals = $955.68       $1,031.2470   $1,031.25   $1,031.30   $1,031.30