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 $77.51   11.354%   $86.3105   $86.31   $86.30   $86.30  
  Purchase #2 $22.95   4.392%   $23.958   $23.96   $23.95   $24.00  
  Purchase #3 $131.72   10.111%   $145.0382   $145.04   $145.05   $145.00  
  Purchase #4 $146.93   10.555%   $162.4385   $162.44   $162.45   $162.40  
  Purchase #5 $213.50   13.452%   $242.22   $242.22   $242.20   $242.20  
  Purchase #6 $138.44   5.759%   $146.4128   $146.41   $146.40   $146.40  
  Purchase #7 $156.78   12.634%   $176.5876   $176.59   $176.60   $176.60  
  7 purchase totals = $887.83       $982.9656   $982.97   $982.95   $982.90