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 $49.34   10.709%   $54.6238   $54.62   $54.60   $54.60  
  Purchase #2 $248.79   5.307%   $261.9933   $261.99   $262.00   $262.00  
  Purchase #3 $94.71   5.853%   $100.2534   $100.25   $100.25   $100.30  
  Purchase #4 $194.31   13.312%   $220.1765   $220.18   $220.20   $220.20  
  Purchase #5 $137.73   7.291%   $147.7719   $147.77   $147.75   $147.80  
  Purchase #6 $145.64   12.342%   $163.6149   $163.61   $163.60   $163.60  
  Purchase #7 $202.55   3.153%   $208.9364   $208.94   $208.95   $208.90  
  7 purchase totals = $1,073.07       $1,157.3702   $1,157.36   $1,157.35   $1,157.40