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 $40.63   6.405%   $43.2324   $43.23   $43.25   $43.20  
  Purchase #2 $211.66   11.431%   $235.8549   $235.85   $235.85   $235.90  
  Purchase #3 $204.72   4.248%   $213.4165   $213.42   $213.40   $213.40  
  Purchase #4 $62.61   8.497%   $67.93   $67.93   $67.95   $67.90  
  Purchase #5 $159.83   12.187%   $179.3085   $179.31   $179.30   $179.30  
  Purchase #6 $199.89   10.360%   $220.5986   $220.60   $220.60   $220.60  
  Purchase #7 $24.90   6.327%   $26.4754   $26.48   $26.50   $26.50  
  7 purchase totals = $904.24       $986.8163   $986.82   $986.85   $986.80