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 $248.46   8.534%   $269.6636   $269.66   $269.65   $269.70  
  Purchase #2 $163.99   4.109%   $170.7283   $170.73   $170.75   $170.70  
  Purchase #3 $56.70   13.658%   $64.4441   $64.44   $64.45   $64.40  
  Purchase #4 $191.40   3.512%   $198.122   $198.12   $198.10   $198.10  
  Purchase #5 $75.28   10.202%   $82.9601   $82.96   $82.95   $83.00  
  Purchase #6 $17.89   7.546%   $19.24   $19.24   $19.25   $19.20  
  Purchase #7 $144.38   11.823%   $161.45   $161.45   $161.45   $161.50  
  7 purchase totals = $898.10       $966.6081   $966.60   $966.60   $966.60