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 $32.53   6.234%   $34.5579   $34.56   $34.55   $34.60  
  Purchase #2 $134.92   5.648%   $142.5403   $142.54   $142.55   $142.50  
  Purchase #3 $109.99   6.527%   $117.169   $117.17   $117.15   $117.20  
  Purchase #4 $8.61   8.552%   $9.3463   $9.35   $9.35   $9.30  
  Purchase #5 $175.92   11.695%   $196.4938   $196.49   $196.50   $196.50  
  Purchase #6 $229.92   9.452%   $251.652   $251.65   $251.65   $251.70  
  Purchase #7 $157.48   3.860%   $163.5587   $163.56   $163.55   $163.60  
  7 purchase totals = $849.37       $915.3180   $915.32   $915.30   $915.40