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 $120.87   8.423%   $131.0509   $131.05   $131.05   $131.10  
  Purchase #2 $93.61   12.109%   $104.9452   $104.95   $104.95   $104.90  
  Purchase #3 $120.56   11.342%   $134.2339   $134.23   $134.25   $134.20  
  Purchase #4 $59.91   5.434%   $63.1655   $63.17   $63.15   $63.20  
  Purchase #5 $139.77   8.716%   $151.9524   $151.95   $151.95   $152.00  
  Purchase #6 $87.69   8.718%   $95.3348   $95.33   $95.35   $95.30  
  Purchase #7 $134.80   4.793%   $141.261   $141.26   $141.25   $141.30  
  7 purchase totals = $757.21       $821.9437   $821.94   $821.95   $822.00