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 $114.69   11.774%   $128.1936   $128.19   $128.20   $128.20  
  Purchase #2 $217.98   11.298%   $242.6074   $242.61   $242.60   $242.60  
  Purchase #3 $175.77   6.166%   $186.608   $186.61   $186.60   $186.60  
  Purchase #4 $176.86   7.426%   $189.9936   $189.99   $190.00   $190.00  
  Purchase #5 $231.79   5.811%   $245.2593   $245.26   $245.25   $245.30  
  Purchase #6 $118.51   6.287%   $125.9607   $125.96   $125.95   $126.00  
  Purchase #7 $82.81   8.331%   $89.7089   $89.71   $89.70   $89.70  
  7 purchase totals = $1,118.41       $1,208.3315   $1,208.33   $1,208.30   $1,208.40