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 $57.37   12.561%   $64.5762   $64.58   $64.60   $64.60  
  Purchase #2 $52.41   9.371%   $57.3213   $57.32   $57.30   $57.30  
  Purchase #3 $249.61   5.238%   $262.6846   $262.68   $262.70   $262.70  
  Purchase #4 $60.63   3.234%   $62.5908   $62.59   $62.60   $62.60  
  Purchase #5 $94.29   13.678%   $107.187   $107.19   $107.20   $107.20  
  Purchase #6 $146.61   7.308%   $157.3243   $157.32   $157.30   $157.30  
  Purchase #7 $232.64   7.826%   $250.8464   $250.85   $250.85   $250.80  
  7 purchase totals = $893.56       $962.5306   $962.53   $962.55   $962.50