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 $241.95   7.552%   $260.2221   $260.22   $260.20   $260.20  
  Purchase #2 $211.82   13.871%   $241.2016   $241.20   $241.20   $241.20  
  Purchase #3 $28.81   13.250%   $32.6273   $32.63   $32.65   $32.60  
  Purchase #4 $191.97   8.658%   $208.5908   $208.59   $208.60   $208.60  
  Purchase #5 $111.83   12.859%   $126.2102   $126.21   $126.20   $126.20  
  Purchase #6 $206.35   11.461%   $229.9998   $230.00   $230.00   $230.00  
  Purchase #7 $15.95   12.749%   $17.9835   $17.98   $18.00   $18.00  
  7 purchase totals = $1,008.68       $1,116.8353   $1,116.83   $1,116.85   $1,116.80