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 $245.63   7.387%   $263.7747   $263.77   $263.75   $263.80  
  Purchase #2 $153.62   13.500%   $174.3587   $174.36   $174.35   $174.40  
  Purchase #3 $42.30   11.351%   $47.1015   $47.10   $47.10   $47.10  
  Purchase #4 $63.81   8.174%   $69.0258   $69.03   $69.05   $69.00  
  Purchase #5 $94.37   7.559%   $101.5034   $101.50   $101.50   $101.50  
  Purchase #6 $208.40   9.813%   $228.8503   $228.85   $228.85   $228.90  
  Purchase #7 $110.80   11.497%   $123.5387   $123.54   $123.55   $123.50  
  7 purchase totals = $918.93       $1,008.1531   $1,008.15   $1,008.15   $1,008.20