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 $237.34   10.706%   $262.7496   $262.75   $262.75   $262.70  
  Purchase #2 $61.84   3.444%   $63.9698   $63.97   $63.95   $64.00  
  Purchase #3 $33.41   10.726%   $36.9936   $36.99   $37.00   $37.00  
  Purchase #4 $75.68   10.531%   $83.6499   $83.65   $83.65   $83.60  
  Purchase #5 $20.91   11.733%   $23.3634   $23.36   $23.35   $23.40  
  Purchase #6 $59.99   7.316%   $64.3789   $64.38   $64.40   $64.40  
  Purchase #7 $34.31   3.735%   $35.5915   $35.59   $35.60   $35.60  
  7 purchase totals = $523.48       $570.6967   $570.69   $570.70   $570.70