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 $245.83   7.827%   $265.0711   $265.07   $265.05   $265.10  
  Purchase #2 $137.72   6.510%   $146.6856   $146.69   $146.70   $146.70  
  Purchase #3 $240.72   3.518%   $249.1885   $249.19   $249.20   $249.20  
  Purchase #4 $232.66   10.668%   $257.4802   $257.48   $257.50   $257.50  
  Purchase #5 $194.70   11.485%   $217.0613   $217.06   $217.05   $217.10  
  Purchase #6 $183.83   9.873%   $201.9795   $201.98   $202.00   $202.00  
  Purchase #7 $234.46   10.464%   $258.9939   $258.99   $259.00   $259.00  
  7 purchase totals = $1,469.92       $1,596.4601   $1,596.46   $1,596.50   $1,596.60