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 $69.42   11.757%   $77.5817   $77.58   $77.60   $77.60  
  Purchase #2 $173.48   5.436%   $182.9104   $182.91   $182.90   $182.90  
  Purchase #3 $15.81   11.451%   $17.6204   $17.62   $17.60   $17.60  
  Purchase #4 $75.25   10.463%   $83.1234   $83.12   $83.10   $83.10  
  Purchase #5 $205.25   8.461%   $222.6162   $222.62   $222.60   $222.60  
  Purchase #6 $86.50   11.315%   $96.2875   $96.29   $96.30   $96.30  
  Purchase #7 $161.75   9.122%   $176.5048   $176.50   $176.50   $176.50  
  7 purchase totals = $787.46       $856.6444   $856.64   $856.60   $856.60