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 $23.59   12.678%   $26.5807   $26.58   $26.60   $26.60  
  Purchase #2 $124.80   7.597%   $134.2811   $134.28   $134.30   $134.30  
  Purchase #3 $157.98   11.182%   $175.6453   $175.65   $175.65   $175.60  
  Purchase #4 $54.57   10.592%   $60.3501   $60.35   $60.35   $60.40  
  Purchase #5 $132.58   5.539%   $139.9236   $139.92   $139.90   $139.90  
  Purchase #6 $174.43   7.544%   $187.589   $187.59   $187.60   $187.60  
  Purchase #7 $208.98   10.278%   $230.459   $230.46   $230.45   $230.50  
  7 purchase totals = $876.93       $954.8288   $954.83   $954.85   $954.90