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 $208.83   8.284%   $226.1295   $226.13   $226.15   $226.10  
  Purchase #2 $104.68   6.391%   $111.3701   $111.37   $111.35   $111.40  
  Purchase #3 $176.49   12.416%   $198.403   $198.40   $198.40   $198.40  
  Purchase #4 $248.92   7.326%   $267.1559   $267.16   $267.15   $267.20  
  Purchase #5 $219.99   12.452%   $247.3832   $247.38   $247.40   $247.40  
  Purchase #6 $119.32   13.764%   $135.7432   $135.74   $135.75   $135.70  
  Purchase #7 $77.35   7.850%   $83.422   $83.42   $83.40   $83.40  
  7 purchase totals = $1,155.58       $1,269.6069   $1,269.60   $1,269.60   $1,269.60