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 $243.80   4.391%   $254.5053   $254.51   $254.50   $254.50  
  Purchase #2 $209.43   4.277%   $218.3873   $218.39   $218.40   $218.40  
  Purchase #3 $115.67   6.416%   $123.0914   $123.09   $123.10   $123.10  
  Purchase #4 $113.61   7.691%   $122.3477   $122.35   $122.35   $122.30  
  Purchase #5 $219.97   5.195%   $231.3974   $231.40   $231.40   $231.40  
  Purchase #6 $59.71   3.350%   $61.7103   $61.71   $61.70   $61.70  
  Purchase #7 $76.46   7.549%   $82.232   $82.23   $82.25   $82.20  
  7 purchase totals = $1,038.65       $1,093.6714   $1,093.68   $1,093.70   $1,093.60