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 $61.25   6.633%   $65.3127   $65.31   $65.30   $65.30  
  Purchase #2 $176.99   13.608%   $201.0748   $201.07   $201.05   $201.10  
  Purchase #3 $63.43   9.635%   $69.5415   $69.54   $69.55   $69.50  
  Purchase #4 $162.41   10.775%   $179.9097   $179.91   $179.90   $179.90  
  Purchase #5 $188.26   8.682%   $204.6047   $204.60   $204.60   $204.60  
  Purchase #6 $148.87   13.249%   $168.5938   $168.59   $168.60   $168.60  
  Purchase #7 $249.91   6.398%   $265.8992   $265.90   $265.90   $265.90  
  7 purchase totals = $1,051.12       $1,154.9364   $1,154.92   $1,154.90   $1,154.90