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 $56.73   11.300%   $63.1405   $63.14   $63.15   $63.10  
  Purchase #2 $131.88   9.145%   $143.9404   $143.94   $143.95   $143.90  
  Purchase #3 $188.47   12.692%   $212.3906   $212.39   $212.40   $212.40  
  Purchase #4 $121.61   9.493%   $133.1544   $133.15   $133.15   $133.20  
  Purchase #5 $118.58   5.331%   $124.9015   $124.90   $124.90   $124.90  
  Purchase #6 $213.95   4.309%   $223.1691   $223.17   $223.15   $223.20  
  Purchase #7 $53.61   5.730%   $56.6819   $56.68   $56.70   $56.70  
  7 purchase totals = $884.83       $957.3784   $957.37   $957.40   $957.40