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 $211.70   13.824%   $240.9654   $240.97   $240.95   $241.00  
  Purchase #2 $59.48   12.484%   $66.9055   $66.91   $66.90   $66.90  
  Purchase #3 $170.31   8.136%   $184.1664   $184.17   $184.15   $184.20  
  Purchase #4 $85.63   7.529%   $92.0771   $92.08   $92.10   $92.10  
  Purchase #5 $98.50   3.104%   $101.5574   $101.56   $101.55   $101.60  
  Purchase #6 $210.30   6.739%   $224.4721   $224.47   $224.45   $224.50  
  Purchase #7 $59.56   12.300%   $66.8859   $66.89   $66.90   $66.90  
  7 purchase totals = $895.48       $977.0298   $977.05   $977.00   $977.20