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 $236.86   4.692%   $247.9735   $247.97   $247.95   $248.00  
  Purchase #2 $61.39   8.564%   $66.6474   $66.65   $66.65   $66.60  
  Purchase #3 $237.96   6.661%   $253.8105   $253.81   $253.80   $253.80  
  Purchase #4 $98.74   6.749%   $105.404   $105.40   $105.40   $105.40  
  Purchase #5 $214.40   3.851%   $222.6565   $222.66   $222.65   $222.70  
  Purchase #6 $116.81   13.412%   $132.4766   $132.48   $132.50   $132.50  
  Purchase #7 $53.63   13.260%   $60.7413   $60.74   $60.75   $60.70  
  7 purchase totals = $1,019.79       $1,089.7098   $1,089.71   $1,089.70   $1,089.70