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 $205.49   8.521%   $222.9998   $223.00   $223.00   $223.00  
  Purchase #2 $142.70   13.508%   $161.9759   $161.98   $162.00   $162.00  
  Purchase #3 $16.26   10.626%   $17.9878   $17.99   $18.00   $18.00  
  Purchase #4 $212.65   11.547%   $237.2047   $237.20   $237.20   $237.20  
  Purchase #5 $58.57   11.219%   $65.141   $65.14   $65.15   $65.10  
  Purchase #6 $22.58   3.167%   $23.2951   $23.30   $23.30   $23.30  
  Purchase #7 $58.83   13.267%   $66.635   $66.64   $66.65   $66.60  
  7 purchase totals = $717.08       $795.2393   $795.25   $795.30   $795.20