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 $123.41   10.472%   $136.3335   $136.33   $136.35   $136.30  
  Purchase #2 $39.57   12.280%   $44.4292   $44.43   $44.45   $44.40  
  Purchase #3 $86.65   4.448%   $90.5042   $90.50   $90.50   $90.50  
  Purchase #4 $184.74   11.360%   $205.7265   $205.73   $205.75   $205.70  
  Purchase #5 $142.48   9.536%   $156.0669   $156.07   $156.05   $156.10  
  Purchase #6 $249.99   4.680%   $261.6895   $261.69   $261.70   $261.70  
  Purchase #7 $50.63   5.625%   $53.4779   $53.48   $53.50   $53.50  
  7 purchase totals = $877.47       $948.2277   $948.23   $948.30   $948.20