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 $235.27   5.373%   $247.9111   $247.91   $247.90   $247.90  
  Purchase #2 $68.79   9.380%   $75.2425   $75.24   $75.25   $75.20  
  Purchase #3 $72.26   11.730%   $80.7361   $80.74   $80.75   $80.70  
  Purchase #4 $54.45   5.797%   $57.6065   $57.61   $57.60   $57.60  
  Purchase #5 $187.74   9.649%   $205.855   $205.86   $205.85   $205.90  
  Purchase #6 $146.39   5.488%   $154.4239   $154.42   $154.40   $154.40  
  Purchase #7 $198.93   4.696%   $208.2718   $208.27   $208.25   $208.30  
  7 purchase totals = $963.83       $1,030.0469   $1,030.05   $1,030.00   $1,030.00