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 $90.98   6.163%   $96.5871   $96.59   $96.60   $96.60  
  Purchase #2 $250.73   5.207%   $263.7855   $263.79   $263.80   $263.80  
  Purchase #3 $134.86   12.758%   $152.0654   $152.07   $152.05   $152.10  
  Purchase #4 $192.69   8.419%   $208.9126   $208.91   $208.90   $208.90  
  Purchase #5 $213.98   13.404%   $242.6619   $242.66   $242.65   $242.70  
  Purchase #6 $160.30   9.320%   $175.24   $175.24   $175.25   $175.20  
  Purchase #7 $41.53   7.518%   $44.6522   $44.65   $44.65   $44.70  
  7 purchase totals = $1,085.07       $1,183.9047   $1,183.91   $1,183.90   $1,184.00