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 $53.42   8.477%   $57.9484   $57.95   $57.95   $57.90  
  Purchase #2 $220.81   9.287%   $241.3166   $241.32   $241.30   $241.30  
  Purchase #3 $248.61   8.149%   $268.8692   $268.87   $268.85   $268.90  
  Purchase #4 $14.66   4.691%   $15.3477   $15.35   $15.35   $15.30  
  Purchase #5 $16.75   4.290%   $17.4686   $17.47   $17.45   $17.50  
  Purchase #6 $234.50   12.759%   $264.4199   $264.42   $264.40   $264.40  
  Purchase #7 $199.32   4.720%   $208.7279   $208.73   $208.75   $208.70  
  7 purchase totals = $988.07       $1,074.0983   $1,074.11   $1,074.05   $1,074.00