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 $241.76   13.568%   $274.562   $274.56   $274.55   $274.60  
  Purchase #2 $92.90   8.675%   $100.9591   $100.96   $100.95   $101.00  
  Purchase #3 $208.67   7.652%   $224.6374   $224.64   $224.65   $224.60  
  Purchase #4 $56.27   5.677%   $59.4644   $59.46   $59.45   $59.50  
  Purchase #5 $49.75   8.529%   $53.9932   $53.99   $54.00   $54.00  
  Purchase #6 $32.77   7.151%   $35.1134   $35.11   $35.10   $35.10  
  Purchase #7 $146.50   6.716%   $156.3389   $156.34   $156.35   $156.30  
  7 purchase totals = $828.62       $905.0684   $905.06   $905.05   $905.10