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 $162.45   11.433%   $181.0229   $181.02   $181.00   $181.00  
  Purchase #2 $153.91   13.156%   $174.1584   $174.16   $174.15   $174.20  
  Purchase #3 $126.32   3.445%   $130.6717   $130.67   $130.65   $130.70  
  Purchase #4 $103.53   10.105%   $113.9917   $113.99   $114.00   $114.00  
  Purchase #5 $240.41   3.495%   $248.8123   $248.81   $248.80   $248.80  
  Purchase #6 $109.27   9.402%   $119.5436   $119.54   $119.55   $119.50  
  Purchase #7 $228.75   12.470%   $257.2751   $257.28   $257.30   $257.30  
  7 purchase totals = $1,124.64       $1,225.4757   $1,225.47   $1,225.45   $1,225.50