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 $232.34   9.473%   $254.3496   $254.35   $254.35   $254.30  
  Purchase #2 $98.48   7.206%   $105.5765   $105.58   $105.60   $105.60  
  Purchase #3 $174.64   9.513%   $191.2535   $191.25   $191.25   $191.30  
  Purchase #4 $132.93   11.247%   $147.8806   $147.88   $147.90   $147.90  
  Purchase #5 $107.46   5.549%   $113.423   $113.42   $113.40   $113.40  
  Purchase #6 $60.71   8.478%   $65.857   $65.86   $65.85   $65.90  
  Purchase #7 $32.66   6.846%   $34.8959   $34.90   $34.90   $34.90  
  7 purchase totals = $839.22       $913.2361   $913.24   $913.25   $913.30