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 $168.91   9.353%   $184.7082   $184.71   $184.70   $184.70  
  Purchase #2 $50.93   8.312%   $55.1633   $55.16   $55.15   $55.20  
  Purchase #3 $118.77   9.714%   $130.3073   $130.31   $130.30   $130.30  
  Purchase #4 $73.77   12.121%   $82.7117   $82.71   $82.70   $82.70  
  Purchase #5 $29.53   3.711%   $30.6259   $30.63   $30.65   $30.60  
  Purchase #6 $218.50   6.501%   $232.7047   $232.70   $232.70   $232.70  
  Purchase #7 $231.39   13.558%   $262.7619   $262.76   $262.75   $262.80  
  7 purchase totals = $891.80       $978.9830   $978.98   $978.95   $979.00