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 $57.92   6.242%   $61.5354   $61.54   $61.55   $61.50  
  Purchase #2 $204.38   4.262%   $213.0907   $213.09   $213.10   $213.10  
  Purchase #3 $246.37   5.836%   $260.7482   $260.75   $260.75   $260.70  
  Purchase #4 $101.52   8.275%   $109.9208   $109.92   $109.90   $109.90  
  Purchase #5 $134.71   7.419%   $144.7041   $144.70   $144.70   $144.70  
  Purchase #6 $217.71   5.329%   $229.3118   $229.31   $229.30   $229.30  
  Purchase #7 $218.81   13.514%   $248.38   $248.38   $248.40   $248.40  
  7 purchase totals = $1,181.42       $1,267.6910   $1,267.69   $1,267.70   $1,267.60