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 $113.97   11.188%   $126.721   $126.72   $126.70   $126.70  
  Purchase #2 $160.93   12.380%   $180.8531   $180.85   $180.85   $180.90  
  Purchase #3 $155.69   4.177%   $162.1932   $162.19   $162.20   $162.20  
  Purchase #4 $178.94   3.835%   $185.8023   $185.80   $185.80   $185.80  
  Purchase #5 $45.45   7.154%   $48.7015   $48.70   $48.70   $48.70  
  Purchase #6 $226.94   9.379%   $248.2247   $248.22   $248.20   $248.20  
  Purchase #7 $194.90   11.622%   $217.5513   $217.55   $217.55   $217.60  
  7 purchase totals = $1,076.82       $1,170.0471   $1,170.03   $1,170.00   $1,170.10