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 $96.42   5.590%   $101.8099   $101.81   $101.80   $101.80  
  Purchase #2 $113.85   8.873%   $123.9519   $123.95   $123.95   $124.00  
  Purchase #3 $196.29   11.194%   $218.2627   $218.26   $218.25   $218.30  
  Purchase #4 $177.28   7.426%   $190.4448   $190.44   $190.45   $190.40  
  Purchase #5 $118.35   13.307%   $134.0988   $134.10   $134.10   $134.10  
  Purchase #6 $241.41   7.642%   $259.8586   $259.86   $259.85   $259.90  
  Purchase #7 $221.47   6.353%   $235.54   $235.54   $235.55   $235.50  
  7 purchase totals = $1,165.07       $1,263.9667   $1,263.96   $1,263.95   $1,264.00