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 $68.73   12.276%   $77.1673   $77.17   $77.15   $77.20  
  Purchase #2 $186.90   4.683%   $195.6525   $195.65   $195.65   $195.70  
  Purchase #3 $158.89   7.724%   $171.1627   $171.16   $171.15   $171.20  
  Purchase #4 $185.61   8.422%   $201.2421   $201.24   $201.25   $201.20  
  Purchase #5 $146.86   12.543%   $165.2806   $165.28   $165.30   $165.30  
  Purchase #6 $191.83   7.704%   $206.6086   $206.61   $206.60   $206.60  
  Purchase #7 $81.95   13.529%   $93.037   $93.04   $93.05   $93.00  
  7 purchase totals = $1,020.77       $1,110.1508   $1,110.15   $1,110.15   $1,110.20