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 $190.41   13.399%   $215.923   $215.92   $215.90   $215.90  
  Purchase #2 $53.99   6.847%   $57.6867   $57.69   $57.70   $57.70  
  Purchase #3 $59.77   6.333%   $63.5552   $63.56   $63.55   $63.60  
  Purchase #4 $202.56   4.401%   $211.4747   $211.47   $211.45   $211.50  
  Purchase #5 $143.26   6.574%   $152.6779   $152.68   $152.70   $152.70  
  Purchase #6 $146.81   13.749%   $166.9949   $166.99   $167.00   $167.00  
  Purchase #7 $71.31   11.549%   $79.5456   $79.55   $79.55   $79.50  
  7 purchase totals = $868.11       $947.8580   $947.86   $947.85   $947.90