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 $87.93   11.557%   $98.0921   $98.09   $98.10   $98.10  
  Purchase #2 $130.83   8.823%   $142.3731   $142.37   $142.35   $142.40  
  Purchase #3 $212.37   12.412%   $238.7294   $238.73   $238.75   $238.70  
  Purchase #4 $13.66   7.577%   $14.695   $14.70   $14.70   $14.70  
  Purchase #5 $62.50   6.525%   $66.5781   $66.58   $66.60   $66.60  
  Purchase #6 $13.28   9.414%   $14.5302   $14.53   $14.55   $14.50  
  Purchase #7 $132.54   8.197%   $143.4043   $143.40   $143.40   $143.40  
  7 purchase totals = $653.11       $718.4022   $718.40   $718.45   $718.40