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 $111.99   13.271%   $126.8522   $126.85   $126.85   $126.90  
  Purchase #2 $78.32   10.667%   $86.6744   $86.67   $86.65   $86.70  
  Purchase #3 $157.96   8.765%   $171.8052   $171.81   $171.80   $171.80  
  Purchase #4 $223.38   4.482%   $233.3919   $233.39   $233.40   $233.40  
  Purchase #5 $155.45   7.249%   $166.7186   $166.72   $166.70   $166.70  
  Purchase #6 $41.64   4.777%   $43.6291   $43.63   $43.65   $43.60  
  Purchase #7 $236.30   11.802%   $264.1881   $264.19   $264.20   $264.20  
  7 purchase totals = $1,005.04       $1,093.2595   $1,093.26   $1,093.25   $1,093.30