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 $114.83   10.346%   $126.7103   $126.71   $126.70   $126.70  
  Purchase #2 $104.41   7.841%   $112.5968   $112.60   $112.60   $112.60  
  Purchase #3 $192.56   6.554%   $205.1804   $205.18   $205.20   $205.20  
  Purchase #4 $46.47   9.335%   $50.808   $50.81   $50.80   $50.80  
  Purchase #5 $68.53   10.744%   $75.8929   $75.89   $75.90   $75.90  
  Purchase #6 $16.59   12.244%   $18.6213   $18.62   $18.60   $18.60  
  Purchase #7 $138.94   11.711%   $155.2113   $155.21   $155.20   $155.20  
  7 purchase totals = $682.33       $745.0210   $745.02   $745.00   $745.00