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 $229.79   13.473%   $260.7496   $260.75   $260.75   $260.70  
  Purchase #2 $24.37   5.111%   $25.6156   $25.62   $25.60   $25.60  
  Purchase #3 $85.25   6.664%   $90.9311   $90.93   $90.95   $90.90  
  Purchase #4 $70.88   6.408%   $75.422   $75.42   $75.40   $75.40  
  Purchase #5 $16.35   11.715%   $18.2654   $18.27   $18.25   $18.30  
  Purchase #6 $24.28   5.835%   $25.6967   $25.70   $25.70   $25.70  
  Purchase #7 $227.60   9.139%   $248.4004   $248.40   $248.40   $248.40  
  7 purchase totals = $678.52       $745.0808   $745.09   $745.05   $745.00