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 $184.26   11.592%   $205.6194   $205.62   $205.60   $205.60  
  Purchase #2 $146.50   12.523%   $164.8462   $164.85   $164.85   $164.80  
  Purchase #3 $238.40   13.643%   $270.9249   $270.92   $270.90   $270.90  
  Purchase #4 $104.32   10.706%   $115.4885   $115.49   $115.50   $115.50  
  Purchase #5 $122.92   12.765%   $138.6107   $138.61   $138.60   $138.60  
  Purchase #6 $150.93   8.402%   $163.6111   $163.61   $163.60   $163.60  
  Purchase #7 $75.28   6.126%   $79.8917   $79.89   $79.90   $79.90  
  7 purchase totals = $1,022.61       $1,138.9925   $1,138.99   $1,138.95   $1,138.90