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 $218.76   9.697%   $239.9732   $239.97   $239.95   $240.00  
  Purchase #2 $44.42   3.744%   $46.0831   $46.08   $46.10   $46.10  
  Purchase #3 $214.54   3.572%   $222.2034   $222.20   $222.20   $222.20  
  Purchase #4 $228.57   5.143%   $240.3254   $240.33   $240.35   $240.30  
  Purchase #5 $49.93   7.454%   $53.6518   $53.65   $53.65   $53.70  
  Purchase #6 $192.53   13.172%   $217.8901   $217.89   $217.90   $217.90  
  Purchase #7 $208.47   7.747%   $224.6202   $224.62   $224.60   $224.60  
  7 purchase totals = $1,157.22       $1,244.7472   $1,244.74   $1,244.75   $1,244.80