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 $241.75   13.214%   $273.6948   $273.69   $273.70   $273.70  
  Purchase #2 $197.87   8.449%   $214.588   $214.59   $214.60   $214.60  
  Purchase #3 $247.41   7.150%   $265.0998   $265.10   $265.10   $265.10  
  Purchase #4 $48.64   6.515%   $51.8089   $51.81   $51.80   $51.80  
  Purchase #5 $233.53   11.801%   $261.0889   $261.09   $261.10   $261.10  
  Purchase #6 $181.25   4.168%   $188.8045   $188.80   $188.80   $188.80  
  Purchase #7 $44.37   5.657%   $46.88   $46.88   $46.90   $46.90  
  7 purchase totals = $1,194.82       $1,301.9649   $1,301.96   $1,302.00   $1,302.00