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 $180.63   7.712%   $194.5602   $194.56   $194.55   $194.60  
  Purchase #2 $192.42   3.675%   $199.4914   $199.49   $199.50   $199.50  
  Purchase #3 $32.58   6.550%   $34.714   $34.71   $34.70   $34.70  
  Purchase #4 $167.95   7.321%   $180.2456   $180.25   $180.25   $180.20  
  Purchase #5 $66.47   9.322%   $72.6663   $72.67   $72.65   $72.70  
  Purchase #6 $136.91   5.545%   $144.5017   $144.50   $144.50   $144.50  
  Purchase #7 $189.97   6.240%   $201.8241   $201.82   $201.80   $201.80  
  7 purchase totals = $966.93       $1,028.0033   $1,028.00   $1,027.95   $1,028.00