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 $185.35   12.736%   $208.9562   $208.96   $208.95   $209.00  
  Purchase #2 $178.25   11.431%   $198.6258   $198.63   $198.65   $198.60  
  Purchase #3 $135.93   9.649%   $149.0459   $149.05   $149.05   $149.00  
  Purchase #4 $153.28   6.701%   $163.5513   $163.55   $163.55   $163.60  
  Purchase #5 $238.37   8.546%   $258.7411   $258.74   $258.75   $258.70  
  Purchase #6 $72.50   8.232%   $78.4682   $78.47   $78.45   $78.50  
  Purchase #7 $8.65   3.338%   $8.9387   $8.94   $8.95   $8.90  
  7 purchase totals = $972.33       $1,066.3272   $1,066.34   $1,066.35   $1,066.30