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 $98.88   8.860%   $107.6408   $107.64   $107.65   $107.60  
  Purchase #2 $222.93   8.257%   $241.3373   $241.34   $241.35   $241.30  
  Purchase #3 $25.66   6.196%   $27.2499   $27.25   $27.25   $27.20  
  Purchase #4 $222.78   13.337%   $252.4922   $252.49   $252.50   $252.50  
  Purchase #5 $15.98   12.395%   $17.9607   $17.96   $17.95   $18.00  
  Purchase #6 $199.34   11.413%   $222.0907   $222.09   $222.10   $222.10  
  Purchase #7 $198.30   4.202%   $206.6326   $206.63   $206.65   $206.60  
  7 purchase totals = $983.87       $1,075.4042   $1,075.40   $1,075.45   $1,075.30