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 $62.50   6.187%   $66.3669   $66.37   $66.35   $66.40  
  Purchase #2 $76.47   9.786%   $83.9534   $83.95   $83.95   $84.00  
  Purchase #3 $94.27   4.528%   $98.5385   $98.54   $98.55   $98.50  
  Purchase #4 $220.71   4.828%   $231.3659   $231.37   $231.35   $231.40  
  Purchase #5 $93.82   3.314%   $96.9292   $96.93   $96.95   $96.90  
  Purchase #6 $98.66   6.533%   $105.1055   $105.11   $105.10   $105.10  
  Purchase #7 $248.25   11.819%   $277.5907   $277.59   $277.60   $277.60  
  7 purchase totals = $894.68       $959.8501   $959.86   $959.85   $959.90