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 $212.87   10.696%   $235.6386   $235.64   $235.65   $235.60  
  Purchase #2 $201.94   12.545%   $227.2734   $227.27   $227.25   $227.30  
  Purchase #3 $233.81   11.738%   $261.2546   $261.25   $261.25   $261.30  
  Purchase #4 $61.99   5.861%   $65.6232   $65.62   $65.60   $65.60  
  Purchase #5 $229.94   13.415%   $260.7865   $260.79   $260.80   $260.80  
  Purchase #6 $208.41   5.545%   $219.9663   $219.97   $219.95   $220.00  
  Purchase #7 $68.39   11.534%   $76.2781   $76.28   $76.30   $76.30  
  7 purchase totals = $1,217.35       $1,346.8207   $1,346.82   $1,346.80   $1,346.90