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 $59.85   6.552%   $63.7714   $63.77   $63.75   $63.80  
  Purchase #2 $207.84   3.335%   $214.7715   $214.77   $214.75   $214.80  
  Purchase #3 $110.52   9.754%   $121.3001   $121.30   $121.30   $121.30  
  Purchase #4 $33.68   9.381%   $36.8395   $36.84   $36.85   $36.80  
  Purchase #5 $130.82   3.293%   $135.1279   $135.13   $135.15   $135.10  
  Purchase #6 $248.46   5.383%   $261.8346   $261.83   $261.85   $261.80  
  Purchase #7 $101.69   11.646%   $113.5328   $113.53   $113.55   $113.50  
  7 purchase totals = $892.86       $947.1778   $947.17   $947.20   $947.10