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 $151.63   7.673%   $163.2646   $163.26   $163.25   $163.30  
  Purchase #2 $227.57   4.135%   $236.98   $236.98   $237.00   $237.00  
  Purchase #3 $71.69   8.273%   $77.6209   $77.62   $77.60   $77.60  
  Purchase #4 $212.47   6.630%   $226.5568   $226.56   $226.55   $226.60  
  Purchase #5 $245.42   6.658%   $261.7601   $261.76   $261.75   $261.80  
  Purchase #6 $209.60   5.543%   $221.2181   $221.22   $221.20   $221.20  
  Purchase #7 $82.29   9.370%   $90.0006   $90.00   $90.00   $90.00  
  7 purchase totals = $1,200.67       $1,277.4011   $1,277.40   $1,277.35   $1,277.50