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 $248.97   5.592%   $262.8924   $262.89   $262.90   $262.90  
  Purchase #2 $25.40   3.201%   $26.2131   $26.21   $26.20   $26.20  
  Purchase #3 $230.44   5.861%   $243.9461   $243.95   $243.95   $243.90  
  Purchase #4 $87.28   4.524%   $91.2285   $91.23   $91.25   $91.20  
  Purchase #5 $125.69   12.680%   $141.6275   $141.63   $141.65   $141.60  
  Purchase #6 $146.56   12.393%   $164.7232   $164.72   $164.70   $164.70  
  Purchase #7 $173.91   6.695%   $185.5533   $185.55   $185.55   $185.60  
  7 purchase totals = $1,038.25       $1,116.1841   $1,116.18   $1,116.20   $1,116.10