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 $23.41   13.243%   $26.5102   $26.51   $26.50   $26.50  
  Purchase #2 $46.59   11.384%   $51.8938   $51.89   $51.90   $51.90  
  Purchase #3 $129.45   7.515%   $139.1782   $139.18   $139.20   $139.20  
  Purchase #4 $235.56   6.563%   $251.0198   $251.02   $251.00   $251.00  
  Purchase #5 $145.96   5.770%   $154.3819   $154.38   $154.40   $154.40  
  Purchase #6 $183.67   13.241%   $207.9897   $207.99   $208.00   $208.00  
  Purchase #7 $99.61   3.829%   $103.4241   $103.42   $103.40   $103.40  
  7 purchase totals = $864.25       $934.3977   $934.39   $934.40   $934.40