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 $34.41   6.147%   $36.5252   $36.53   $36.55   $36.50  
  Purchase #2 $114.25   9.173%   $124.7302   $124.73   $124.75   $124.70  
  Purchase #3 $196.93   13.628%   $223.7676   $223.77   $223.75   $223.80  
  Purchase #4 $247.81   12.529%   $278.8581   $278.86   $278.85   $278.90  
  Purchase #5 $105.99   8.855%   $115.3754   $115.38   $115.40   $115.40  
  Purchase #6 $118.97   12.284%   $133.5843   $133.58   $133.60   $133.60  
  Purchase #7 $232.66   3.705%   $241.2801   $241.28   $241.30   $241.30  
  7 purchase totals = $1,051.02       $1,154.1209   $1,154.13   $1,154.20   $1,154.20