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 $49.25   3.154%   $50.8033   $50.80   $50.80   $50.80  
  Purchase #2 $233.32   6.262%   $247.9305   $247.93   $247.95   $247.90  
  Purchase #3 $146.62   6.854%   $156.6693   $156.67   $156.65   $156.70  
  Purchase #4 $188.89   12.392%   $212.2972   $212.30   $212.30   $212.30  
  Purchase #5 $56.95   11.368%   $63.4241   $63.42   $63.40   $63.40  
  Purchase #6 $85.63   6.311%   $91.0341   $91.03   $91.05   $91.00  
  Purchase #7 $54.43   11.299%   $60.58   $60.58   $60.60   $60.60  
  7 purchase totals = $815.09       $882.7385   $882.73   $882.75   $882.70