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 $34.63   10.688%   $38.3313   $38.33   $38.35   $38.30  
  Purchase #2 $146.68   3.369%   $151.6216   $151.62   $151.60   $151.60  
  Purchase #3 $223.97   5.688%   $236.7094   $236.71   $236.70   $236.70  
  Purchase #4 $91.75   7.504%   $98.6349   $98.63   $98.65   $98.60  
  Purchase #5 $135.88   5.384%   $143.1958   $143.20   $143.20   $143.20  
  Purchase #6 $212.77   4.727%   $222.8276   $222.83   $222.85   $222.80  
  Purchase #7 $54.59   9.383%   $59.7122   $59.71   $59.70   $59.70  
  7 purchase totals = $900.27       $951.0328   $951.03   $951.05   $950.90