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 $185.33   8.679%   $201.4148   $201.41   $201.40   $201.40  
  Purchase #2 $228.42   5.154%   $240.1928   $240.19   $240.20   $240.20  
  Purchase #3 $171.61   6.386%   $182.569   $182.57   $182.55   $182.60  
  Purchase #4 $135.78   12.833%   $153.2046   $153.20   $153.20   $153.20  
  Purchase #5 $67.90   8.159%   $73.44   $73.44   $73.45   $73.40  
  Purchase #6 $98.93   8.116%   $106.9592   $106.96   $106.95   $107.00  
  Purchase #7 $222.75   12.493%   $250.5782   $250.58   $250.60   $250.60  
  7 purchase totals = $1,110.72       $1,208.3586   $1,208.35   $1,208.35   $1,208.40