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 $247.48   6.758%   $264.2047   $264.20   $264.20   $264.20  
  Purchase #2 $145.44   7.366%   $156.1531   $156.15   $156.15   $156.20  
  Purchase #3 $124.33   7.632%   $133.8189   $133.82   $133.80   $133.80  
  Purchase #4 $187.95   10.463%   $207.6152   $207.62   $207.60   $207.60  
  Purchase #5 $79.89   8.139%   $86.3922   $86.39   $86.40   $86.40  
  Purchase #6 $104.78   9.247%   $114.469   $114.47   $114.45   $114.50  
  Purchase #7 $205.26   3.713%   $212.8813   $212.88   $212.90   $212.90  
  7 purchase totals = $1,095.13       $1,175.5344   $1,175.53   $1,175.50   $1,175.60