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 $54.58   5.257%   $57.4493   $57.45   $57.45   $57.40  
  Purchase #2 $204.82   8.455%   $222.1375   $222.14   $222.15   $222.10  
  Purchase #3 $33.75   8.328%   $36.5607   $36.56   $36.55   $36.60  
  Purchase #4 $132.32   7.124%   $141.7465   $141.75   $141.75   $141.70  
  Purchase #5 $236.26   5.755%   $249.8568   $249.86   $249.85   $249.90  
  Purchase #6 $232.98   11.615%   $260.0406   $260.04   $260.05   $260.00  
  Purchase #7 $236.66   10.802%   $262.224   $262.22   $262.20   $262.20  
  7 purchase totals = $1,131.37       $1,230.0154   $1,230.02   $1,230.00   $1,229.90