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 $58.99   13.267%   $66.8162   $66.82   $66.80   $66.80  
  Purchase #2 $214.73   4.379%   $224.133   $224.13   $224.15   $224.10  
  Purchase #3 $238.49   3.652%   $247.1997   $247.20   $247.20   $247.20  
  Purchase #4 $48.59   4.688%   $50.8679   $50.87   $50.85   $50.90  
  Purchase #5 $250.71   6.458%   $266.9009   $266.90   $266.90   $266.90  
  Purchase #6 $211.77   6.446%   $225.4207   $225.42   $225.40   $225.40  
  Purchase #7 $87.69   11.226%   $97.5341   $97.53   $97.55   $97.50  
  7 purchase totals = $1,110.97       $1,178.8725   $1,178.87   $1,178.85   $1,178.80