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 $24.82   5.620%   $26.2149   $26.21   $26.20   $26.20  
  Purchase #2 $83.83   4.548%   $87.6426   $87.64   $87.65   $87.60  
  Purchase #3 $152.73   9.271%   $166.8896   $166.89   $166.90   $166.90  
  Purchase #4 $37.40   6.589%   $39.8643   $39.86   $39.85   $39.90  
  Purchase #5 $174.40   5.439%   $183.8856   $183.89   $183.90   $183.90  
  Purchase #6 $126.99   6.143%   $134.791   $134.79   $134.80   $134.80  
  Purchase #7 $24.82   5.375%   $26.1541   $26.15   $26.15   $26.20  
  7 purchase totals = $624.99       $665.4421   $665.43   $665.45   $665.50