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 $23.39   11.480%   $26.0752   $26.08   $26.10   $26.10  
  Purchase #2 $235.97   3.381%   $243.9481   $243.95   $243.95   $243.90  
  Purchase #3 $58.89   5.552%   $62.1596   $62.16   $62.15   $62.20  
  Purchase #4 $239.39   5.285%   $252.0418   $252.04   $252.05   $252.00  
  Purchase #5 $84.91   10.533%   $93.8536   $93.85   $93.85   $93.90  
  Purchase #6 $165.26   7.645%   $177.8941   $177.89   $177.90   $177.90  
  Purchase #7 $68.27   8.466%   $74.0497   $74.05   $74.05   $74.00  
  7 purchase totals = $876.08       $930.0221   $930.02   $930.05   $930.00