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 $61.58   13.156%   $69.6815   $69.68   $69.70   $69.70  
  Purchase #2 $70.99   9.284%   $77.5807   $77.58   $77.60   $77.60  
  Purchase #3 $32.98   3.699%   $34.1999   $34.20   $34.20   $34.20  
  Purchase #4 $164.70   9.419%   $180.2131   $180.21   $180.20   $180.20  
  Purchase #5 $205.98   7.275%   $220.965   $220.97   $220.95   $221.00  
  Purchase #6 $107.40   6.563%   $114.4487   $114.45   $114.45   $114.40  
  Purchase #7 $40.99   4.388%   $42.7886   $42.79   $42.80   $42.80  
  7 purchase totals = $684.62       $739.8775   $739.88   $739.90   $739.90