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 $213.68   5.824%   $226.1247   $226.12   $226.10   $226.10  
  Purchase #2 $127.92   8.822%   $139.2051   $139.21   $139.20   $139.20  
  Purchase #3 $45.80   7.351%   $49.1668   $49.17   $49.15   $49.20  
  Purchase #4 $166.82   5.354%   $175.7515   $175.75   $175.75   $175.80  
  Purchase #5 $135.71   3.590%   $140.582   $140.58   $140.60   $140.60  
  Purchase #6 $79.55   8.773%   $86.5289   $86.53   $86.55   $86.50  
  Purchase #7 $223.55   10.807%   $247.709   $247.71   $247.70   $247.70  
  7 purchase totals = $993.03       $1,065.0680   $1,065.07   $1,065.05   $1,065.10