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 $232.85   10.218%   $256.6426   $256.64   $256.65   $256.60  
  Purchase #2 $108.54   4.744%   $113.6891   $113.69   $113.70   $113.70  
  Purchase #3 $44.66   11.300%   $49.7066   $49.71   $49.70   $49.70  
  Purchase #4 $153.46   5.398%   $161.7438   $161.74   $161.75   $161.70  
  Purchase #5 $105.78   11.808%   $118.2705   $118.27   $118.25   $118.30  
  Purchase #6 $61.37   8.295%   $66.4606   $66.46   $66.45   $66.50  
  Purchase #7 $65.79   9.125%   $71.7933   $71.79   $71.80   $71.80  
  7 purchase totals = $772.45       $838.3065   $838.30   $838.30   $838.30