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 $57.49   9.480%   $62.9401   $62.94   $62.95   $62.90  
  Purchase #2 $128.76   11.625%   $143.7284   $143.73   $143.75   $143.70  
  Purchase #3 $233.26   6.617%   $248.6948   $248.69   $248.70   $248.70  
  Purchase #4 $9.46   10.568%   $10.4597   $10.46   $10.45   $10.50  
  Purchase #5 $111.51   12.720%   $125.6941   $125.69   $125.70   $125.70  
  Purchase #6 $216.60   5.754%   $229.0632   $229.06   $229.05   $229.10  
  Purchase #7 $188.38   13.134%   $213.1218   $213.12   $213.10   $213.10  
  7 purchase totals = $945.46       $1,033.7021   $1,033.69   $1,033.70   $1,033.70