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 $230.46   11.495%   $256.9514   $256.95   $256.95   $257.00  
  Purchase #2 $95.28   9.484%   $104.3164   $104.32   $104.30   $104.30  
  Purchase #3 $163.26   5.803%   $172.734   $172.73   $172.75   $172.70  
  Purchase #4 $199.28   7.488%   $214.2021   $214.20   $214.20   $214.20  
  Purchase #5 $68.36   6.791%   $73.0023   $73.00   $73.00   $73.00  
  Purchase #6 $82.95   12.374%   $93.2142   $93.21   $93.20   $93.20  
  Purchase #7 $41.61   10.189%   $45.8496   $45.85   $45.85   $45.80  
  7 purchase totals = $881.20       $960.2700   $960.26   $960.25   $960.20