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 $206.45   13.822%   $234.9855   $234.99   $235.00   $235.00  
  Purchase #2 $81.26   10.172%   $89.5258   $89.53   $89.55   $89.50  
  Purchase #3 $225.59   7.532%   $242.5814   $242.58   $242.60   $242.60  
  Purchase #4 $112.69   12.383%   $126.6444   $126.64   $126.65   $126.60  
  Purchase #5 $232.81   7.589%   $250.478   $250.48   $250.50   $250.50  
  Purchase #6 $206.67   3.253%   $213.393   $213.39   $213.40   $213.40  
  Purchase #7 $244.55   7.110%   $261.9375   $261.94   $261.95   $261.90  
  7 purchase totals = $1,310.02       $1,419.5456   $1,419.55   $1,419.65   $1,419.50