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 $56.95   5.511%   $60.0885   $60.09   $60.10   $60.10  
  Purchase #2 $54.41   5.872%   $57.605   $57.61   $57.60   $57.60  
  Purchase #3 $131.98   9.626%   $144.6844   $144.68   $144.70   $144.70  
  Purchase #4 $229.99   10.261%   $253.5893   $253.59   $253.60   $253.60  
  Purchase #5 $48.89   4.107%   $50.8979   $50.90   $50.90   $50.90  
  Purchase #6 $44.99   10.500%   $49.714   $49.71   $49.70   $49.70  
  Purchase #7 $166.30   13.114%   $188.1086   $188.11   $188.10   $188.10  
  7 purchase totals = $733.51       $804.6877   $804.69   $804.70   $804.70