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 $156.76   5.280%   $165.0369   $165.04   $165.05   $165.00  
  Purchase #2 $187.81   9.699%   $206.0257   $206.03   $206.05   $206.00  
  Purchase #3 $224.83   5.474%   $237.1372   $237.14   $237.15   $237.10  
  Purchase #4 $61.75   8.546%   $67.0272   $67.03   $67.05   $67.00  
  Purchase #5 $104.35   12.844%   $117.7527   $117.75   $117.75   $117.80  
  Purchase #6 $243.97   9.242%   $266.5177   $266.52   $266.50   $266.50  
  Purchase #7 $183.56   12.434%   $206.3839   $206.38   $206.40   $206.40  
  7 purchase totals = $1,163.03       $1,265.8813   $1,265.89   $1,265.95   $1,265.80