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 $104.48   6.262%   $111.0225   $111.02   $111.00   $111.00  
  Purchase #2 $134.33   10.296%   $148.1606   $148.16   $148.15   $148.20  
  Purchase #3 $75.85   3.619%   $78.595   $78.60   $78.60   $78.60  
  Purchase #4 $241.57   11.767%   $269.9955   $270.00   $270.00   $270.00  
  Purchase #5 $243.36   5.743%   $257.3362   $257.34   $257.35   $257.30  
  Purchase #6 $31.69   10.754%   $35.0979   $35.10   $35.10   $35.10  
  Purchase #7 $32.68   6.601%   $34.8372   $34.84   $34.85   $34.80  
  7 purchase totals = $863.96       $935.0449   $935.06   $935.05   $935.00