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 $188.50   8.788%   $205.0654   $205.07   $205.05   $205.10  
  Purchase #2 $97.67   13.272%   $110.6328   $110.63   $110.65   $110.60  
  Purchase #3 $144.95   11.238%   $161.2395   $161.24   $161.25   $161.20  
  Purchase #4 $14.48   4.764%   $15.1698   $15.17   $15.15   $15.20  
  Purchase #5 $192.28   7.785%   $207.249   $207.25   $207.25   $207.20  
  Purchase #6 $220.98   12.235%   $248.0169   $248.02   $248.00   $248.00  
  Purchase #7 $196.46   11.364%   $218.7857   $218.79   $218.80   $218.80  
  7 purchase totals = $1,055.32       $1,166.1591   $1,166.17   $1,166.15   $1,166.10