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 $234.61   13.388%   $266.0196   $266.02   $266.00   $266.00  
  Purchase #2 $11.27   13.258%   $12.7642   $12.76   $12.75   $12.80  
  Purchase #3 $154.61   6.178%   $164.1618   $164.16   $164.15   $164.20  
  Purchase #4 $23.81   10.304%   $26.2634   $26.26   $26.25   $26.30  
  Purchase #5 $158.35   12.659%   $178.3955   $178.40   $178.40   $178.40  
  Purchase #6 $223.72   5.131%   $235.1991   $235.20   $235.20   $235.20  
  Purchase #7 $174.27   4.721%   $182.4973   $182.50   $182.50   $182.50  
  7 purchase totals = $980.64       $1,065.3009   $1,065.30   $1,065.25   $1,065.40