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 $142.84   9.179%   $155.9513   $155.95   $155.95   $156.00  
  Purchase #2 $168.98   7.714%   $182.0151   $182.02   $182.00   $182.00  
  Purchase #3 $181.49   8.338%   $196.6226   $196.62   $196.60   $196.60  
  Purchase #4 $224.66   10.871%   $249.0828   $249.08   $249.10   $249.10  
  Purchase #5 $108.56   4.239%   $113.1619   $113.16   $113.15   $113.20  
  Purchase #6 $176.51   12.315%   $198.2472   $198.25   $198.25   $198.20  
  Purchase #7 $64.49   10.555%   $71.2969   $71.30   $71.30   $71.30  
  7 purchase totals = $1,067.53       $1,166.3778   $1,166.38   $1,166.35   $1,166.40