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 $24.55   6.148%   $26.0593   $26.06   $26.05   $26.10  
  Purchase #2 $174.57   6.522%   $185.9555   $185.96   $185.95   $186.00  
  Purchase #3 $131.45   6.302%   $139.734   $139.73   $139.75   $139.70  
  Purchase #4 $123.61   12.674%   $139.2763   $139.28   $139.30   $139.30  
  Purchase #5 $188.30   5.152%   $198.0012   $198.00   $198.00   $198.00  
  Purchase #6 $188.29   7.684%   $202.7582   $202.76   $202.75   $202.80  
  Purchase #7 $64.41   4.202%   $67.1165   $67.12   $67.10   $67.10  
  7 purchase totals = $895.18       $958.9010   $958.91   $958.90   $959.00