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 $105.86   12.874%   $119.4884   $119.49   $119.50   $119.50  
  Purchase #2 $186.76   11.732%   $208.6707   $208.67   $208.65   $208.70  
  Purchase #3 $70.53   8.139%   $76.2704   $76.27   $76.25   $76.30  
  Purchase #4 $202.48   4.497%   $211.5855   $211.59   $211.60   $211.60  
  Purchase #5 $170.94   12.821%   $192.8562   $192.86   $192.85   $192.90  
  Purchase #6 $250.73   11.135%   $278.6488   $278.65   $278.65   $278.60  
  Purchase #7 $23.75   7.752%   $25.5911   $25.59   $25.60   $25.60  
  7 purchase totals = $1,011.05       $1,113.1111   $1,113.12   $1,113.10   $1,113.20