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 $201.86   3.183%   $208.2852   $208.29   $208.30   $208.30  
  Purchase #2 $38.26   11.262%   $42.5688   $42.57   $42.55   $42.60  
  Purchase #3 $37.38   5.791%   $39.5447   $39.54   $39.55   $39.50  
  Purchase #4 $84.63   9.730%   $92.8645   $92.86   $92.85   $92.90  
  Purchase #5 $202.89   4.351%   $211.7177   $211.72   $211.70   $211.70  
  Purchase #6 $67.70   13.363%   $76.7468   $76.75   $76.75   $76.70  
  Purchase #7 $178.89   10.804%   $198.2173   $198.22   $198.20   $198.20  
  7 purchase totals = $811.61       $869.9450   $869.95   $869.90   $869.90