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 $81.58   5.395%   $85.9812   $85.98   $86.00   $86.00  
  Purchase #2 $50.91   10.575%   $56.2937   $56.29   $56.30   $56.30  
  Purchase #3 $86.89   7.811%   $93.677   $93.68   $93.70   $93.70  
  Purchase #4 $113.25   9.232%   $123.7052   $123.71   $123.70   $123.70  
  Purchase #5 $123.59   9.332%   $135.1234   $135.12   $135.10   $135.10  
  Purchase #6 $84.70   13.324%   $95.9854   $95.99   $96.00   $96.00  
  Purchase #7 $14.63   6.619%   $15.5984   $15.60   $15.60   $15.60  
  7 purchase totals = $555.55       $606.3643   $606.37   $606.40   $606.40