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 $204.99   10.137%   $225.7698   $225.77   $225.75   $225.80  
  Purchase #2 $14.39   7.530%   $15.4736   $15.47   $15.45   $15.50  
  Purchase #3 $23.51   10.861%   $26.0634   $26.06   $26.05   $26.10  
  Purchase #4 $85.76   5.459%   $90.4416   $90.44   $90.45   $90.40  
  Purchase #5 $190.60   5.796%   $201.6472   $201.65   $201.65   $201.60  
  Purchase #6 $11.82   3.589%   $12.2442   $12.24   $12.25   $12.20  
  Purchase #7 $244.30   7.241%   $261.9898   $261.99   $262.00   $262.00  
  7 purchase totals = $775.37       $833.6296   $833.62   $833.60   $833.60