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 $61.40   9.365%   $67.1501   $67.15   $67.15   $67.20  
  Purchase #2 $235.84   4.446%   $246.3254   $246.33   $246.35   $246.30  
  Purchase #3 $164.69   7.755%   $177.4617   $177.46   $177.45   $177.50  
  Purchase #4 $26.53   13.290%   $30.0558   $30.06   $30.05   $30.10  
  Purchase #5 $24.32   3.685%   $25.2162   $25.22   $25.20   $25.20  
  Purchase #6 $104.68   7.628%   $112.665   $112.67   $112.65   $112.70  
  Purchase #7 $49.85   11.602%   $55.6336   $55.63   $55.65   $55.60  
  7 purchase totals = $667.31       $714.5078   $714.52   $714.50   $714.60