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 $14.65   4.776%   $15.3497   $15.35   $15.35   $15.30  
  Purchase #2 $177.66   11.762%   $198.5564   $198.56   $198.55   $198.60  
  Purchase #3 $242.48   6.167%   $257.4337   $257.43   $257.45   $257.40  
  Purchase #4 $127.56   13.358%   $144.5995   $144.60   $144.60   $144.60  
  Purchase #5 $163.75   7.405%   $175.8757   $175.88   $175.90   $175.90  
  Purchase #6 $34.42   10.250%   $37.9481   $37.95   $37.95   $37.90  
  Purchase #7 $230.63   5.441%   $243.1786   $243.18   $243.20   $243.20  
  7 purchase totals = $991.15       $1,072.9417   $1,072.95   $1,073.00   $1,072.90