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 $236.25   4.471%   $246.8127   $246.81   $246.80   $246.80  
  Purchase #2 $179.94   3.256%   $185.7988   $185.80   $185.80   $185.80  
  Purchase #3 $67.82   8.691%   $73.7142   $73.71   $73.70   $73.70  
  Purchase #4 $90.74   11.867%   $101.5081   $101.51   $101.50   $101.50  
  Purchase #5 $207.78   6.788%   $221.8841   $221.88   $221.90   $221.90  
  Purchase #6 $108.51   6.870%   $115.9646   $115.96   $115.95   $116.00  
  Purchase #7 $81.76   12.312%   $91.8263   $91.83   $91.85   $91.80  
  7 purchase totals = $972.80       $1,037.5088   $1,037.50   $1,037.50   $1,037.50