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 $76.98   12.361%   $86.4955   $86.50   $86.50   $86.50  
  Purchase #2 $69.71   13.551%   $79.1564   $79.16   $79.15   $79.20  
  Purchase #3 $32.28   12.286%   $36.2459   $36.25   $36.25   $36.20  
  Purchase #4 $249.55   7.449%   $268.139   $268.14   $268.15   $268.10  
  Purchase #5 $193.99   7.214%   $207.9844   $207.98   $208.00   $208.00  
  Purchase #6 $160.43   6.602%   $171.0216   $171.02   $171.00   $171.00  
  Purchase #7 $78.88   12.393%   $88.6556   $88.66   $88.65   $88.70  
  7 purchase totals = $861.82       $937.6984   $937.71   $937.70   $937.70