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 $12.87   12.793%   $14.5165   $14.52   $14.50   $14.50  
  Purchase #2 $232.89   7.724%   $250.8784   $250.88   $250.90   $250.90  
  Purchase #3 $239.60   7.489%   $257.5436   $257.54   $257.55   $257.50  
  Purchase #4 $16.67   5.198%   $17.5365   $17.54   $17.55   $17.50  
  Purchase #5 $57.90   8.787%   $62.9877   $62.99   $63.00   $63.00  
  Purchase #6 $162.46   6.249%   $172.6121   $172.61   $172.60   $172.60  
  Purchase #7 $17.36   8.122%   $18.77   $18.77   $18.75   $18.80  
  7 purchase totals = $739.75       $794.8448   $794.85   $794.85   $794.80