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 $21.64   10.321%   $23.8735   $23.87   $23.85   $23.90  
  Purchase #2 $109.53   9.192%   $119.598   $119.60   $119.60   $119.60  
  Purchase #3 $229.85   8.260%   $248.8356   $248.84   $248.85   $248.80  
  Purchase #4 $37.26   11.618%   $41.5889   $41.59   $41.60   $41.60  
  Purchase #5 $213.67   5.611%   $225.659   $225.66   $225.65   $225.70  
  Purchase #6 $86.67   13.331%   $98.224   $98.22   $98.20   $98.20  
  Purchase #7 $186.45   10.545%   $206.1112   $206.11   $206.10   $206.10  
  7 purchase totals = $885.07       $963.8902   $963.89   $963.85   $963.90