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 $206.67   8.221%   $223.6603   $223.66   $223.65   $223.70  
  Purchase #2 $101.92   12.516%   $114.6763   $114.68   $114.70   $114.70  
  Purchase #3 $121.61   11.190%   $135.2182   $135.22   $135.20   $135.20  
  Purchase #4 $57.43   5.358%   $60.5071   $60.51   $60.50   $60.50  
  Purchase #5 $105.84   8.611%   $114.9539   $114.95   $114.95   $115.00  
  Purchase #6 $150.76   5.629%   $159.2463   $159.25   $159.25   $159.20  
  Purchase #7 $137.25   9.821%   $150.7293   $150.73   $150.75   $150.70  
  7 purchase totals = $881.48       $958.9914   $959.00   $959.00   $959.00