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 $247.54   8.223%   $267.8952   $267.90   $267.90   $267.90  
  Purchase #2 $52.83   9.174%   $57.6766   $57.68   $57.70   $57.70  
  Purchase #3 $39.49   8.704%   $42.9272   $42.93   $42.95   $42.90  
  Purchase #4 $108.27   9.134%   $118.1594   $118.16   $118.15   $118.20  
  Purchase #5 $158.38   4.564%   $165.6085   $165.61   $165.60   $165.60  
  Purchase #6 $232.90   6.125%   $247.1651   $247.17   $247.15   $247.20  
  Purchase #7 $201.40   12.766%   $227.1107   $227.11   $227.10   $227.10  
  7 purchase totals = $1,040.81       $1,126.5427   $1,126.56   $1,126.55   $1,126.60