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 $86.42   7.622%   $93.0069   $93.01   $93.00   $93.00  
  Purchase #2 $224.81   10.750%   $248.9771   $248.98   $249.00   $249.00  
  Purchase #3 $238.70   6.460%   $254.12   $254.12   $254.10   $254.10  
  Purchase #4 $33.74   3.433%   $34.8983   $34.90   $34.90   $34.90  
  Purchase #5 $169.71   4.579%   $177.481   $177.48   $177.50   $177.50  
  Purchase #6 $249.66   10.180%   $275.0754   $275.08   $275.10   $275.10  
  Purchase #7 $162.76   10.601%   $180.0142   $180.01   $180.00   $180.00  
  7 purchase totals = $1,165.80       $1,263.5729   $1,263.58   $1,263.60   $1,263.60