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 $165.26   10.741%   $183.0106   $183.01   $183.00   $183.00  
  Purchase #2 $186.26   8.542%   $202.1703   $202.17   $202.15   $202.20  
  Purchase #3 $69.92   3.528%   $72.3868   $72.39   $72.40   $72.40  
  Purchase #4 $228.66   10.187%   $251.9536   $251.95   $251.95   $252.00  
  Purchase #5 $244.46   3.696%   $253.4952   $253.50   $253.50   $253.50  
  Purchase #6 $79.88   8.609%   $86.7569   $86.76   $86.75   $86.80  
  Purchase #7 $207.93   9.189%   $227.0367   $227.04   $227.05   $227.00  
  7 purchase totals = $1,182.37       $1,276.8101   $1,276.82   $1,276.80   $1,276.90