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 $106.81   10.533%   $118.0603   $118.06   $118.05   $118.10  
  Purchase #2 $67.74   7.572%   $72.8693   $72.87   $72.85   $72.90  
  Purchase #3 $71.77   8.172%   $77.635   $77.64   $77.65   $77.60  
  Purchase #4 $53.48   7.797%   $57.6498   $57.65   $57.65   $57.60  
  Purchase #5 $226.61   11.277%   $252.1648   $252.16   $252.15   $252.20  
  Purchase #6 $63.47   4.200%   $66.1357   $66.14   $66.15   $66.10  
  Purchase #7 $218.86   7.340%   $234.9243   $234.92   $234.90   $234.90  
  7 purchase totals = $808.74       $879.4392   $879.44   $879.40   $879.40