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 $130.43   3.306%   $134.742   $134.74   $134.75   $134.70  
  Purchase #2 $248.78   8.433%   $269.7596   $269.76   $269.75   $269.80  
  Purchase #3 $151.85   13.740%   $172.7142   $172.71   $172.70   $172.70  
  Purchase #4 $199.33   4.344%   $207.9889   $207.99   $208.00   $208.00  
  Purchase #5 $109.40   8.447%   $118.641   $118.64   $118.65   $118.60  
  Purchase #6 $101.86   6.149%   $108.1234   $108.12   $108.10   $108.10  
  Purchase #7 $236.34   4.803%   $247.6914   $247.69   $247.70   $247.70  
  7 purchase totals = $1,177.99       $1,259.6605   $1,259.65   $1,259.65   $1,259.60