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 $24.60   5.773%   $26.0202   $26.02   $26.00   $26.00  
  Purchase #2 $21.41   9.784%   $23.5048   $23.50   $23.50   $23.50  
  Purchase #3 $109.93   8.138%   $118.8761   $118.88   $118.90   $118.90  
  Purchase #4 $190.74   5.252%   $200.7577   $200.76   $200.75   $200.80  
  Purchase #5 $79.83   5.625%   $84.3204   $84.32   $84.30   $84.30  
  Purchase #6 $161.88   6.170%   $171.868   $171.87   $171.85   $171.90  
  Purchase #7 $158.30   5.204%   $166.5379   $166.54   $166.55   $166.50  
  7 purchase totals = $746.69       $791.8851   $791.89   $791.85   $791.90