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 $166.82   10.451%   $184.2544   $184.25   $184.25   $184.30  
  Purchase #2 $154.63   13.399%   $175.3489   $175.35   $175.35   $175.30  
  Purchase #3 $49.55   5.484%   $52.2673   $52.27   $52.25   $52.30  
  Purchase #4 $15.84   4.553%   $16.5612   $16.56   $16.55   $16.60  
  Purchase #5 $222.73   6.618%   $237.4703   $237.47   $237.45   $237.50  
  Purchase #6 $101.85   3.516%   $105.431   $105.43   $105.45   $105.40  
  Purchase #7 $13.99   10.772%   $15.497   $15.50   $15.50   $15.50  
  7 purchase totals = $725.41       $786.8301   $786.83   $786.80   $786.90