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 $201.34   6.732%   $214.8942   $214.89   $214.90   $214.90  
  Purchase #2 $33.71   5.778%   $35.6578   $35.66   $35.65   $35.70  
  Purchase #3 $67.70   4.828%   $70.9686   $70.97   $70.95   $71.00  
  Purchase #4 $9.99   6.140%   $10.6034   $10.60   $10.60   $10.60  
  Purchase #5 $75.43   6.296%   $80.1791   $80.18   $80.20   $80.20  
  Purchase #6 $68.74   4.786%   $72.0299   $72.03   $72.05   $72.00  
  Purchase #7 $249.81   12.326%   $280.6016   $280.60   $280.60   $280.60  
  7 purchase totals = $706.72       $764.9346   $764.93   $764.95   $765.00