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 $183.32   13.871%   $208.7483   $208.75   $208.75   $208.70  
  Purchase #2 $61.88   10.482%   $68.3663   $68.37   $68.35   $68.40  
  Purchase #3 $31.26   5.796%   $33.0718   $33.07   $33.05   $33.10  
  Purchase #4 $73.77   12.420%   $82.9322   $82.93   $82.95   $82.90  
  Purchase #5 $242.32   9.466%   $265.258   $265.26   $265.25   $265.30  
  Purchase #6 $32.83   4.692%   $34.3704   $34.37   $34.35   $34.40  
  Purchase #7 $168.39   7.826%   $181.5682   $181.57   $181.55   $181.60  
  7 purchase totals = $793.77       $874.3152   $874.32   $874.25   $874.40