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 $205.54   6.513%   $218.9268   $218.93   $218.95   $218.90  
  Purchase #2 $10.63   4.849%   $11.1454   $11.15   $11.15   $11.10  
  Purchase #3 $68.51   6.705%   $73.1036   $73.10   $73.10   $73.10  
  Purchase #4 $84.62   11.215%   $94.1101   $94.11   $94.10   $94.10  
  Purchase #5 $223.77   9.861%   $245.836   $245.84   $245.85   $245.80  
  Purchase #6 $177.28   4.868%   $185.91   $185.91   $185.90   $185.90  
  Purchase #7 $136.95   13.811%   $155.8642   $155.86   $155.85   $155.90  
  7 purchase totals = $907.30       $984.8961   $984.90   $984.90   $984.80