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 $61.88   7.677%   $66.6305   $66.63   $66.65   $66.60  
  Purchase #2 $237.53   5.649%   $250.9481   $250.95   $250.95   $250.90  
  Purchase #3 $72.40   7.483%   $77.8177   $77.82   $77.80   $77.80  
  Purchase #4 $13.86   11.526%   $15.4575   $15.46   $15.45   $15.50  
  Purchase #5 $174.32   3.804%   $180.9511   $180.95   $180.95   $181.00  
  Purchase #6 $149.72   13.821%   $170.4128   $170.41   $170.40   $170.40  
  Purchase #7 $32.37   3.329%   $33.4476   $33.45   $33.45   $33.40  
  7 purchase totals = $742.08       $795.6653   $795.67   $795.65   $795.60