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 $67.42   13.679%   $76.6424   $76.64   $76.65   $76.60  
  Purchase #2 $233.95   13.413%   $265.3297   $265.33   $265.35   $265.30  
  Purchase #3 $242.82   12.751%   $273.782   $273.78   $273.80   $273.80  
  Purchase #4 $126.71   12.189%   $142.1547   $142.15   $142.15   $142.20  
  Purchase #5 $163.26   6.160%   $173.3168   $173.32   $173.30   $173.30  
  Purchase #6 $30.38   12.798%   $34.268   $34.27   $34.25   $34.30  
  Purchase #7 $174.66   7.856%   $188.3813   $188.38   $188.40   $188.40  
  7 purchase totals = $1,039.20       $1,153.8749   $1,153.87   $1,153.90   $1,153.90