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 $54.47   12.438%   $61.245   $61.25   $61.25   $61.20  
  Purchase #2 $215.46   10.247%   $237.5382   $237.54   $237.55   $237.50  
  Purchase #3 $56.43   10.812%   $62.5312   $62.53   $62.55   $62.50  
  Purchase #4 $60.40   11.212%   $67.172   $67.17   $67.15   $67.20  
  Purchase #5 $79.28   13.856%   $90.265   $90.27   $90.25   $90.30  
  Purchase #6 $132.69   12.804%   $149.6796   $149.68   $149.70   $149.70  
  Purchase #7 $219.44   7.215%   $235.2726   $235.27   $235.25   $235.30  
  7 purchase totals = $818.17       $903.7036   $903.71   $903.70   $903.70