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 $55.81   11.170%   $62.044   $62.04   $62.05   $62.00  
  Purchase #2 $82.41   11.300%   $91.7223   $91.72   $91.70   $91.70  
  Purchase #3 $112.77   3.353%   $116.5512   $116.55   $116.55   $116.60  
  Purchase #4 $75.44   7.553%   $81.138   $81.14   $81.15   $81.10  
  Purchase #5 $227.79   7.561%   $245.0132   $245.01   $245.00   $245.00  
  Purchase #6 $127.77   9.641%   $140.0883   $140.09   $140.10   $140.10  
  Purchase #7 $215.69   3.210%   $222.6136   $222.61   $222.60   $222.60  
  7 purchase totals = $897.68       $959.1706   $959.16   $959.15   $959.10