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 $59.93   5.484%   $63.2166   $63.22   $63.20   $63.20  
  Purchase #2 $142.62   9.567%   $156.2645   $156.26   $156.25   $156.30  
  Purchase #3 $221.93   11.841%   $248.2087   $248.21   $248.20   $248.20  
  Purchase #4 $234.42   4.508%   $244.9877   $244.99   $245.00   $245.00  
  Purchase #5 $85.41   10.756%   $94.5967   $94.60   $94.60   $94.60  
  Purchase #6 $107.34   13.279%   $121.5937   $121.59   $121.60   $121.60  
  Purchase #7 $29.40   4.518%   $30.7283   $30.73   $30.75   $30.70  
  7 purchase totals = $881.05       $959.5962   $959.60   $959.60   $959.60