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 $56.69   7.764%   $61.0914   $61.09   $61.10   $61.10  
  Purchase #2 $31.68   12.342%   $35.5899   $35.59   $35.60   $35.60  
  Purchase #3 $109.59   6.263%   $116.4536   $116.45   $116.45   $116.50  
  Purchase #4 $166.53   7.610%   $179.2029   $179.20   $179.20   $179.20  
  Purchase #5 $240.92   7.212%   $258.2952   $258.30   $258.30   $258.30  
  Purchase #6 $190.78   9.313%   $208.5473   $208.55   $208.55   $208.50  
  Purchase #7 $60.41   7.726%   $65.0773   $65.08   $65.10   $65.10  
  7 purchase totals = $856.60       $924.2576   $924.26   $924.30   $924.30