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 $247.64   5.732%   $261.8347   $261.83   $261.85   $261.80  
  Purchase #2 $217.32   9.683%   $238.3631   $238.36   $238.35   $238.40  
  Purchase #3 $95.85   10.156%   $105.5845   $105.58   $105.60   $105.60  
  Purchase #4 $23.44   8.345%   $25.3961   $25.40   $25.40   $25.40  
  Purchase #5 $22.56   11.748%   $25.2103   $25.21   $25.20   $25.20  
  Purchase #6 $128.67   6.386%   $136.8869   $136.89   $136.90   $136.90  
  Purchase #7 $214.43   11.566%   $239.231   $239.23   $239.25   $239.20  
  7 purchase totals = $949.91       $1,032.5066   $1,032.50   $1,032.55   $1,032.50