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 $182.85   11.662%   $204.174   $204.17   $204.15   $204.20  
  Purchase #2 $49.89   9.776%   $54.7672   $54.77   $54.75   $54.80  
  Purchase #3 $42.47   7.592%   $45.6943   $45.69   $45.70   $45.70  
  Purchase #4 $175.40   10.451%   $193.7311   $193.73   $193.75   $193.70  
  Purchase #5 $26.77   6.434%   $28.4924   $28.49   $28.50   $28.50  
  Purchase #6 $8.93   13.738%   $10.1568   $10.16   $10.15   $10.20  
  Purchase #7 $218.44   10.442%   $241.2495   $241.25   $241.25   $241.20  
  7 purchase totals = $704.75       $778.2653   $778.26   $778.25   $778.30