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 $204.93   13.466%   $232.5259   $232.53   $232.55   $232.50  
  Purchase #2 $221.78   8.760%   $241.2079   $241.21   $241.20   $241.20  
  Purchase #3 $248.47   6.669%   $265.0405   $265.04   $265.05   $265.00  
  Purchase #4 $171.68   4.544%   $179.4811   $179.48   $179.50   $179.50  
  Purchase #5 $91.87   12.581%   $103.4282   $103.43   $103.45   $103.40  
  Purchase #6 $38.89   5.139%   $40.8886   $40.89   $40.90   $40.90  
  Purchase #7 $155.54   12.566%   $175.0852   $175.09   $175.10   $175.10  
  7 purchase totals = $1,133.16       $1,237.6574   $1,237.67   $1,237.75   $1,237.60