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 $76.90   10.464%   $84.9468   $84.95   $84.95   $84.90  
  Purchase #2 $114.88   4.109%   $119.6004   $119.60   $119.60   $119.60  
  Purchase #3 $178.58   11.545%   $199.1971   $199.20   $199.20   $199.20  
  Purchase #4 $73.44   6.678%   $78.3443   $78.34   $78.35   $78.30  
  Purchase #5 $229.42   10.819%   $254.2409   $254.24   $254.25   $254.20  
  Purchase #6 $72.96   13.516%   $82.8213   $82.82   $82.80   $82.80  
  Purchase #7 $56.25   11.579%   $62.7632   $62.76   $62.75   $62.80  
  7 purchase totals = $802.43       $881.9140   $881.91   $881.90   $881.80