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 $181.67   13.543%   $206.2736   $206.27   $206.25   $206.30  
  Purchase #2 $237.41   7.669%   $255.617   $255.62   $255.60   $255.60  
  Purchase #3 $170.65   10.523%   $188.6075   $188.61   $188.60   $188.60  
  Purchase #4 $204.54   6.131%   $217.0803   $217.08   $217.10   $217.10  
  Purchase #5 $225.78   10.824%   $250.2184   $250.22   $250.20   $250.20  
  Purchase #6 $9.90   11.134%   $11.0023   $11.00   $11.00   $11.00  
  Purchase #7 $166.83   11.774%   $186.4726   $186.47   $186.45   $186.50  
  7 purchase totals = $1,196.78       $1,315.2717   $1,315.27   $1,315.20   $1,315.30