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 $203.42   11.604%   $227.0249   $227.02   $227.00   $227.00  
  Purchase #2 $213.85   10.267%   $235.806   $235.81   $235.80   $235.80  
  Purchase #3 $171.74   10.211%   $189.2764   $189.28   $189.30   $189.30  
  Purchase #4 $171.33   8.724%   $186.2768   $186.28   $186.30   $186.30  
  Purchase #5 $65.80   4.848%   $68.99   $68.99   $69.00   $69.00  
  Purchase #6 $13.43   13.760%   $15.278   $15.28   $15.30   $15.30  
  Purchase #7 $16.44   13.231%   $18.6152   $18.62   $18.60   $18.60  
  7 purchase totals = $856.01       $941.2673   $941.28   $941.30   $941.30