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 $92.83   6.221%   $98.605   $98.61   $98.60   $98.60  
  Purchase #2 $126.55   10.526%   $139.8707   $139.87   $139.85   $139.90  
  Purchase #3 $54.86   3.669%   $56.8728   $56.87   $56.85   $56.90  
  Purchase #4 $57.50   6.127%   $61.023   $61.02   $61.00   $61.00  
  Purchase #5 $105.50   11.167%   $117.2812   $117.28   $117.30   $117.30  
  Purchase #6 $131.70   11.781%   $147.2156   $147.22   $147.20   $147.20  
  Purchase #7 $127.34   8.557%   $138.2365   $138.24   $138.25   $138.20  
  7 purchase totals = $696.28       $759.1048   $759.11   $759.05   $759.10