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 $224.85   11.143%   $249.905   $249.91   $249.90   $249.90  
  Purchase #2 $239.41   9.808%   $262.8913   $262.89   $262.90   $262.90  
  Purchase #3 $51.38   12.310%   $57.7049   $57.70   $57.70   $57.70  
  Purchase #4 $173.29   4.718%   $181.4658   $181.47   $181.45   $181.50  
  Purchase #5 $242.61   10.169%   $267.281   $267.28   $267.30   $267.30  
  Purchase #6 $14.30   8.430%   $15.5055   $15.51   $15.50   $15.50  
  Purchase #7 $21.87   11.223%   $24.3245   $24.32   $24.30   $24.30  
  7 purchase totals = $967.71       $1,059.0780   $1,059.08   $1,059.05   $1,059.10