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 $38.45   8.403%   $41.681   $41.68   $41.70   $41.70  
  Purchase #2 $130.32   3.186%   $134.472   $134.47   $134.45   $134.50  
  Purchase #3 $56.53   12.529%   $63.6126   $63.61   $63.60   $63.60  
  Purchase #4 $250.55   6.186%   $266.049   $266.05   $266.05   $266.00  
  Purchase #5 $67.35   12.693%   $75.8987   $75.90   $75.90   $75.90  
  Purchase #6 $124.59   11.460%   $138.868   $138.87   $138.85   $138.90  
  Purchase #7 $150.80   3.720%   $156.4098   $156.41   $156.40   $156.40  
  7 purchase totals = $818.59       $876.9911   $876.99   $876.95   $877.00