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 $164.92   10.648%   $182.4807   $182.48   $182.50   $182.50  
  Purchase #2 $170.38   9.791%   $187.0619   $187.06   $187.05   $187.10  
  Purchase #3 $54.74   6.376%   $58.2302   $58.23   $58.25   $58.20  
  Purchase #4 $60.63   4.868%   $63.5815   $63.58   $63.60   $63.60  
  Purchase #5 $232.36   11.235%   $258.4656   $258.47   $258.45   $258.50  
  Purchase #6 $192.58   4.861%   $201.9413   $201.94   $201.95   $201.90  
  Purchase #7 $71.88   3.654%   $74.5065   $74.51   $74.50   $74.50  
  7 purchase totals = $947.49       $1,026.2677   $1,026.27   $1,026.30   $1,026.30