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 $22.70   5.770%   $24.0098   $24.01   $24.00   $24.00  
  Purchase #2 $43.36   12.819%   $48.9183   $48.92   $48.90   $48.90  
  Purchase #3 $127.45   3.809%   $132.3046   $132.30   $132.30   $132.30  
  Purchase #4 $107.99   10.573%   $119.4078   $119.41   $119.40   $119.40  
  Purchase #5 $204.98   3.457%   $212.0662   $212.07   $212.05   $212.10  
  Purchase #6 $230.69   12.551%   $259.6439   $259.64   $259.65   $259.60  
  Purchase #7 $54.30   11.768%   $60.69   $60.69   $60.70   $60.70  
  7 purchase totals = $791.47       $857.0406   $857.04   $857.00   $857.00