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 $25.63   4.269%   $26.7241   $26.72   $26.70   $26.70  
  Purchase #2 $85.58   7.500%   $91.9985   $92.00   $92.00   $92.00  
  Purchase #3 $63.29   10.267%   $69.788   $69.79   $69.80   $69.80  
  Purchase #4 $72.34   5.770%   $76.514   $76.51   $76.50   $76.50  
  Purchase #5 $113.85   10.593%   $125.9101   $125.91   $125.90   $125.90  
  Purchase #6 $220.77   9.235%   $241.1581   $241.16   $241.15   $241.20  
  Purchase #7 $25.26   6.597%   $26.9264   $26.93   $26.95   $26.90  
  7 purchase totals = $606.72       $659.0192   $659.02   $659.00   $659.00