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 $227.87   11.143%   $253.2616   $253.26   $253.25   $253.30  
  Purchase #2 $79.61   4.171%   $82.9305   $82.93   $82.95   $82.90  
  Purchase #3 $53.91   4.220%   $56.185   $56.19   $56.20   $56.20  
  Purchase #4 $81.65   12.396%   $91.7713   $91.77   $91.75   $91.80  
  Purchase #5 $107.88   9.292%   $117.9042   $117.90   $117.90   $117.90  
  Purchase #6 $134.69   7.510%   $144.8052   $144.81   $144.80   $144.80  
  Purchase #7 $197.66   7.210%   $211.9113   $211.91   $211.90   $211.90  
  7 purchase totals = $883.27       $958.7691   $958.77   $958.75   $958.80