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 $61.36   9.806%   $67.377   $67.38   $67.40   $67.40  
  Purchase #2 $74.93   5.840%   $79.3059   $79.31   $79.30   $79.30  
  Purchase #3 $119.80   5.223%   $126.0572   $126.06   $126.05   $126.10  
  Purchase #4 $58.77   4.854%   $61.6227   $61.62   $61.60   $61.60  
  Purchase #5 $26.70   6.856%   $28.5306   $28.53   $28.55   $28.50  
  Purchase #6 $38.45   3.788%   $39.9065   $39.91   $39.90   $39.90  
  Purchase #7 $106.56   5.687%   $112.6201   $112.62   $112.60   $112.60  
  7 purchase totals = $486.57       $515.4200   $515.43   $515.40   $515.40