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 $22.47   8.207%   $24.3141   $24.31   $24.30   $24.30  
  Purchase #2 $182.87   13.855%   $208.2066   $208.21   $208.20   $208.20  
  Purchase #3 $65.99   6.197%   $70.0794   $70.08   $70.10   $70.10  
  Purchase #4 $77.91   13.853%   $88.7029   $88.70   $88.70   $88.70  
  Purchase #5 $241.76   7.819%   $260.6632   $260.66   $260.65   $260.70  
  Purchase #6 $103.71   3.366%   $107.2009   $107.20   $107.20   $107.20  
  Purchase #7 $181.94   6.103%   $193.0438   $193.04   $193.05   $193.00  
  7 purchase totals = $876.65       $952.2109   $952.20   $952.20   $952.20