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 $216.51   8.216%   $234.2985   $234.30   $234.30   $234.30  
  Purchase #2 $179.81   7.734%   $193.7165   $193.72   $193.70   $193.70  
  Purchase #3 $208.40   10.305%   $229.8756   $229.88   $229.90   $229.90  
  Purchase #4 $238.96   6.724%   $255.0277   $255.03   $255.05   $255.00  
  Purchase #5 $58.54   13.446%   $66.4113   $66.41   $66.40   $66.40  
  Purchase #6 $110.37   8.631%   $119.896   $119.90   $119.90   $119.90  
  Purchase #7 $152.42   5.863%   $161.3564   $161.36   $161.35   $161.40  
  7 purchase totals = $1,165.01       $1,260.5820   $1,260.60   $1,260.60   $1,260.60