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 $188.57   10.636%   $208.6263   $208.63   $208.65   $208.60  
  Purchase #2 $248.58   8.216%   $269.0033   $269.00   $269.00   $269.00  
  Purchase #3 $111.94   4.552%   $117.0355   $117.04   $117.05   $117.00  
  Purchase #4 $90.98   13.639%   $103.3888   $103.39   $103.40   $103.40  
  Purchase #5 $107.41   10.117%   $118.2767   $118.28   $118.30   $118.30  
  Purchase #6 $217.95   3.542%   $225.6698   $225.67   $225.65   $225.70  
  Purchase #7 $20.68   9.208%   $22.5842   $22.58   $22.60   $22.60  
  7 purchase totals = $986.11       $1,064.5846   $1,064.59   $1,064.65   $1,064.60