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 $174.32   11.628%   $194.5899   $194.59   $194.60   $194.60  
  Purchase #2 $239.42   6.230%   $254.3359   $254.34   $254.35   $254.30  
  Purchase #3 $208.85   9.819%   $229.357   $229.36   $229.35   $229.40  
  Purchase #4 $30.61   3.126%   $31.5669   $31.57   $31.55   $31.60  
  Purchase #5 $57.54   12.479%   $64.7204   $64.72   $64.70   $64.70  
  Purchase #6 $159.45   10.827%   $176.7137   $176.71   $176.70   $176.70  
  Purchase #7 $235.32   12.627%   $265.0339   $265.03   $265.05   $265.00  
  7 purchase totals = $1,105.51       $1,216.3177   $1,216.32   $1,216.30   $1,216.30