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 $77.55   8.697%   $84.2945   $84.29   $84.30   $84.30  
  Purchase #2 $248.35   7.519%   $267.0234   $267.02   $267.00   $267.00  
  Purchase #3 $66.86   12.744%   $75.3806   $75.38   $75.40   $75.40  
  Purchase #4 $51.98   7.652%   $55.9575   $55.96   $55.95   $56.00  
  Purchase #5 $249.76   6.559%   $266.1418   $266.14   $266.15   $266.10  
  Purchase #6 $80.75   6.153%   $85.7185   $85.72   $85.70   $85.70  
  Purchase #7 $182.68   13.565%   $207.4605   $207.46   $207.45   $207.50  
  7 purchase totals = $957.93       $1,041.9768   $1,041.97   $1,041.95   $1,042.00