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 $224.86   12.154%   $252.1895   $252.19   $252.20   $252.20  
  Purchase #2 $81.79   5.498%   $86.2868   $86.29   $86.30   $86.30  
  Purchase #3 $99.92   7.690%   $107.6038   $107.60   $107.60   $107.60  
  Purchase #4 $226.40   9.665%   $248.2816   $248.28   $248.30   $248.30  
  Purchase #5 $132.96   4.127%   $138.4473   $138.45   $138.45   $138.40  
  Purchase #6 $47.86   3.702%   $49.6318   $49.63   $49.65   $49.60  
  Purchase #7 $128.42   12.448%   $144.4057   $144.41   $144.40   $144.40  
  7 purchase totals = $942.21       $1,026.8465   $1,026.85   $1,026.90   $1,026.80