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 $206.80   9.660%   $226.7769   $226.78   $226.80   $226.80  
  Purchase #2 $216.49   9.301%   $236.6257   $236.63   $236.65   $236.60  
  Purchase #3 $197.80   11.705%   $220.9525   $220.95   $220.95   $221.00  
  Purchase #4 $73.94   5.543%   $78.0385   $78.04   $78.05   $78.00  
  Purchase #5 $238.38   6.210%   $253.1834   $253.18   $253.20   $253.20  
  Purchase #6 $225.94   7.526%   $242.9442   $242.94   $242.95   $242.90  
  Purchase #7 $46.82   5.426%   $49.3605   $49.36   $49.35   $49.40  
  7 purchase totals = $1,206.17       $1,307.8817   $1,307.88   $1,307.95   $1,307.90