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 $85.87   12.801%   $96.8622   $96.86   $96.85   $96.90  
  Purchase #2 $199.38   8.363%   $216.0541   $216.05   $216.05   $216.10  
  Purchase #3 $59.80   5.533%   $63.1087   $63.11   $63.10   $63.10  
  Purchase #4 $202.95   13.725%   $230.8049   $230.80   $230.80   $230.80  
  Purchase #5 $75.78   8.852%   $82.488   $82.49   $82.50   $82.50  
  Purchase #6 $108.69   7.676%   $117.033   $117.03   $117.05   $117.00  
  Purchase #7 $26.64   3.628%   $27.6065   $27.61   $27.60   $27.60  
  7 purchase totals = $759.11       $833.9574   $833.95   $833.95   $834.00