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 $188.35   10.161%   $207.4882   $207.49   $207.50   $207.50  
  Purchase #2 $128.63   5.716%   $135.9825   $135.98   $136.00   $136.00  
  Purchase #3 $32.80   10.532%   $36.2545   $36.25   $36.25   $36.30  
  Purchase #4 $86.50   9.277%   $94.5246   $94.52   $94.50   $94.50  
  Purchase #5 $229.55   13.817%   $261.2669   $261.27   $261.25   $261.30  
  Purchase #6 $159.42   3.312%   $164.7   $164.70   $164.70   $164.70  
  Purchase #7 $164.86   12.855%   $186.0528   $186.05   $186.05   $186.10  
  7 purchase totals = $990.11       $1,086.2695   $1,086.26   $1,086.25   $1,086.40