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 $53.44   4.722%   $55.9634   $55.96   $55.95   $56.00  
  Purchase #2 $225.42   13.543%   $255.9486   $255.95   $255.95   $255.90  
  Purchase #3 $136.45   11.871%   $152.648   $152.65   $152.65   $152.60  
  Purchase #4 $35.36   3.543%   $36.6128   $36.61   $36.60   $36.60  
  Purchase #5 $76.93   5.138%   $80.8827   $80.88   $80.90   $80.90  
  Purchase #6 $235.55   7.273%   $252.6816   $252.68   $252.70   $252.70  
  Purchase #7 $111.39   5.181%   $117.1611   $117.16   $117.15   $117.20  
  7 purchase totals = $874.54       $951.8982   $951.89   $951.90   $951.90