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 $48.95   5.569%   $51.676   $51.68   $51.70   $51.70  
  Purchase #2 $223.62   3.574%   $231.6122   $231.61   $231.60   $231.60  
  Purchase #3 $127.30   4.288%   $132.7586   $132.76   $132.75   $132.80  
  Purchase #4 $114.26   9.867%   $125.534   $125.53   $125.55   $125.50  
  Purchase #5 $163.94   4.469%   $171.2665   $171.27   $171.25   $171.30  
  Purchase #6 $103.57   12.593%   $116.6126   $116.61   $116.60   $116.60  
  Purchase #7 $202.50   13.398%   $229.631   $229.63   $229.65   $229.60  
  7 purchase totals = $984.14       $1,059.0909   $1,059.09   $1,059.10   $1,059.10