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 $242.72   3.391%   $250.9506   $250.95   $250.95   $251.00  
  Purchase #2 $93.27   12.171%   $104.6219   $104.62   $104.60   $104.60  
  Purchase #3 $64.30   13.706%   $73.113   $73.11   $73.10   $73.10  
  Purchase #4 $210.63   3.783%   $218.5981   $218.60   $218.60   $218.60  
  Purchase #5 $77.65   5.354%   $81.8074   $81.81   $81.80   $81.80  
  Purchase #6 $93.67   13.266%   $106.0963   $106.10   $106.10   $106.10  
  Purchase #7 $103.25   13.372%   $117.0566   $117.06   $117.05   $117.10  
  7 purchase totals = $885.49       $952.2439   $952.25   $952.20   $952.30