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 $239.44   11.734%   $267.5359   $267.54   $267.55   $267.50  
  Purchase #2 $142.41   9.371%   $155.7552   $155.76   $155.75   $155.80  
  Purchase #3 $177.93   3.572%   $184.2857   $184.29   $184.30   $184.30  
  Purchase #4 $168.84   10.803%   $187.0798   $187.08   $187.10   $187.10  
  Purchase #5 $174.28   4.622%   $182.3352   $182.34   $182.35   $182.30  
  Purchase #6 $248.81   11.459%   $277.3211   $277.32   $277.30   $277.30  
  Purchase #7 $186.71   9.199%   $203.8855   $203.89   $203.90   $203.90  
  7 purchase totals = $1,338.42       $1,458.1984   $1,458.22   $1,458.25   $1,458.20