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 $240.64   10.139%   $265.0385   $265.04   $265.05   $265.00  
  Purchase #2 $244.95   6.553%   $261.0016   $261.00   $261.00   $261.00  
  Purchase #3 $50.41   11.277%   $56.0947   $56.09   $56.10   $56.10  
  Purchase #4 $189.61   9.287%   $207.2191   $207.22   $207.20   $207.20  
  Purchase #5 $162.76   9.125%   $177.6119   $177.61   $177.60   $177.60  
  Purchase #6 $65.65   8.121%   $70.9814   $70.98   $71.00   $71.00  
  Purchase #7 $10.53   11.505%   $11.7415   $11.74   $11.75   $11.70  
  7 purchase totals = $964.55       $1,049.6887   $1,049.68   $1,049.70   $1,049.60