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 $56.27   12.269%   $63.1738   $63.17   $63.15   $63.20  
  Purchase #2 $117.49   9.490%   $128.6398   $128.64   $128.65   $128.60  
  Purchase #3 $6.48   12.274%   $7.2754   $7.28   $7.30   $7.30  
  Purchase #4 $176.75   8.569%   $191.8957   $191.90   $191.90   $191.90  
  Purchase #5 $163.56   6.158%   $173.632   $173.63   $173.65   $173.60  
  Purchase #6 $237.54   10.327%   $262.0708   $262.07   $262.05   $262.10  
  Purchase #7 $113.77   8.388%   $123.313   $123.31   $123.30   $123.30  
  7 purchase totals = $871.86       $950.0005   $950.00   $950.00   $950.00