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 $54.98   8.846%   $59.8435   $59.84   $59.85   $59.80  
  Purchase #2 $168.78   5.565%   $178.1726   $178.17   $178.15   $178.20  
  Purchase #3 $248.86   10.549%   $275.1122   $275.11   $275.10   $275.10  
  Purchase #4 $122.61   10.668%   $135.69   $135.69   $135.70   $135.70  
  Purchase #5 $239.56   9.601%   $262.5602   $262.56   $262.55   $262.60  
  Purchase #6 $152.75   13.191%   $172.8993   $172.90   $172.90   $172.90  
  Purchase #7 $86.91   13.682%   $98.801   $98.80   $98.80   $98.80  
  7 purchase totals = $1,074.45       $1,183.0788   $1,183.07   $1,183.05   $1,183.10