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 $58.71   13.797%   $66.8102   $66.81   $66.80   $66.80  
  Purchase #2 $162.41   9.508%   $177.8519   $177.85   $177.85   $177.90  
  Purchase #3 $77.84   7.307%   $83.5278   $83.53   $83.55   $83.50  
  Purchase #4 $116.42   7.261%   $124.8733   $124.87   $124.85   $124.90  
  Purchase #5 $207.82   13.150%   $235.1483   $235.15   $235.15   $235.10  
  Purchase #6 $39.57   13.456%   $44.8945   $44.89   $44.90   $44.90  
  Purchase #7 $23.66   8.769%   $25.7347   $25.73   $25.75   $25.70  
  7 purchase totals = $686.43       $758.8407   $758.83   $758.85   $758.80