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 $126.90   11.858%   $141.9478   $141.95   $141.95   $141.90  
  Purchase #2 $174.65   11.289%   $194.3662   $194.37   $194.35   $194.40  
  Purchase #3 $21.85   6.631%   $23.2989   $23.30   $23.30   $23.30  
  Purchase #4 $248.25   10.190%   $273.5467   $273.55   $273.55   $273.50  
  Purchase #5 $69.95   13.416%   $79.3345   $79.33   $79.35   $79.30  
  Purchase #6 $206.95   13.672%   $235.2442   $235.24   $235.25   $235.20  
  Purchase #7 $21.32   3.159%   $21.9935   $21.99   $22.00   $22.00  
  7 purchase totals = $869.87       $969.7318   $969.73   $969.75   $969.60