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 $203.41   10.422%   $224.6094   $224.61   $224.60   $224.60  
  Purchase #2 $128.81   11.206%   $143.2444   $143.24   $143.25   $143.20  
  Purchase #3 $98.31   13.488%   $111.5701   $111.57   $111.55   $111.60  
  Purchase #4 $166.94   5.785%   $176.5975   $176.60   $176.60   $176.60  
  Purchase #5 $105.70   7.843%   $113.9901   $113.99   $114.00   $114.00  
  Purchase #6 $173.45   7.369%   $186.2315   $186.23   $186.25   $186.20  
  Purchase #7 $161.63   5.750%   $170.9237   $170.92   $170.90   $170.90  
  7 purchase totals = $1,038.25       $1,127.1667   $1,127.16   $1,127.15   $1,127.10