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 $67.64   5.226%   $71.1749   $71.17   $71.15   $71.20  
  Purchase #2 $214.45   11.800%   $239.7551   $239.76   $239.75   $239.80  
  Purchase #3 $82.58   13.147%   $93.4368   $93.44   $93.45   $93.40  
  Purchase #4 $209.31   6.542%   $223.0031   $223.00   $223.00   $223.00  
  Purchase #5 $65.49   7.728%   $70.5511   $70.55   $70.55   $70.60  
  Purchase #6 $78.66   11.181%   $87.455   $87.46   $87.45   $87.50  
  Purchase #7 $53.67   6.642%   $57.2348   $57.23   $57.25   $57.20  
  7 purchase totals = $771.80       $842.6108   $842.61   $842.60   $842.70