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 $184.59   5.783%   $195.2648   $195.26   $195.25   $195.30  
  Purchase #2 $105.97   9.398%   $115.9291   $115.93   $115.95   $115.90  
  Purchase #3 $35.45   7.414%   $38.0783   $38.08   $38.10   $38.10  
  Purchase #4 $79.43   8.787%   $86.4095   $86.41   $86.40   $86.40  
  Purchase #5 $165.83   10.429%   $183.1244   $183.12   $183.10   $183.10  
  Purchase #6 $53.49   13.663%   $60.7983   $60.80   $60.80   $60.80  
  Purchase #7 $38.60   8.826%   $42.0068   $42.01   $42.00   $42.00  
  7 purchase totals = $663.36       $721.6112   $721.61   $721.60   $721.60