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 $87.42   13.111%   $98.8816   $98.88   $98.90   $98.90  
  Purchase #2 $240.93   10.357%   $265.8831   $265.88   $265.90   $265.90  
  Purchase #3 $41.90   4.128%   $43.6296   $43.63   $43.65   $43.60  
  Purchase #4 $167.76   13.229%   $189.953   $189.95   $189.95   $190.00  
  Purchase #5 $45.57   5.646%   $48.1429   $48.14   $48.15   $48.10  
  Purchase #6 $188.33   13.366%   $213.5022   $213.50   $213.50   $213.50  
  Purchase #7 $76.26   9.104%   $83.2027   $83.20   $83.20   $83.20  
  7 purchase totals = $848.17       $943.1951   $943.18   $943.25   $943.20