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 $68.99   13.460%   $78.2761   $78.28   $78.30   $78.30  
  Purchase #2 $102.55   7.708%   $110.4546   $110.45   $110.45   $110.50  
  Purchase #3 $91.76   6.491%   $97.7161   $97.72   $97.70   $97.70  
  Purchase #4 $162.45   5.383%   $171.1947   $171.19   $171.20   $171.20  
  Purchase #5 $207.91   3.492%   $215.1702   $215.17   $215.15   $215.20  
  Purchase #6 $34.99   13.438%   $39.692   $39.69   $39.70   $39.70  
  Purchase #7 $21.53   13.542%   $24.4456   $24.45   $24.45   $24.40  
  7 purchase totals = $690.18       $736.9493   $736.95   $736.95   $737.00