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 $177.28   12.302%   $199.089   $199.09   $199.10   $199.10  
  Purchase #2 $248.28   7.411%   $266.68   $266.68   $266.70   $266.70  
  Purchase #3 $56.45   4.293%   $58.8734   $58.87   $58.85   $58.90  
  Purchase #4 $95.54   11.863%   $106.8739   $106.87   $106.85   $106.90  
  Purchase #5 $43.38   13.185%   $49.0997   $49.10   $49.10   $49.10  
  Purchase #6 $190.99   5.667%   $201.8134   $201.81   $201.80   $201.80  
  Purchase #7 $43.77   4.133%   $45.579   $45.58   $45.60   $45.60  
  7 purchase totals = $855.69       $928.0084   $928.00   $928.00   $928.10