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 $231.83   13.355%   $262.7909   $262.79   $262.80   $262.80  
  Purchase #2 $28.69   6.407%   $30.5282   $30.53   $30.55   $30.50  
  Purchase #3 $126.75   6.265%   $134.6909   $134.69   $134.70   $134.70  
  Purchase #4 $10.54   5.796%   $11.1509   $11.15   $11.15   $11.20  
  Purchase #5 $176.56   11.145%   $196.2376   $196.24   $196.25   $196.20  
  Purchase #6 $242.94   8.664%   $263.9883   $263.99   $264.00   $264.00  
  Purchase #7 $92.79   12.414%   $104.309   $104.31   $104.30   $104.30  
  7 purchase totals = $910.10       $1,003.6958   $1,003.70   $1,003.75   $1,003.70