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 $30.37   13.843%   $34.5741   $34.57   $34.55   $34.60  
  Purchase #2 $214.99   6.490%   $228.9429   $228.94   $228.95   $228.90  
  Purchase #3 $147.98   4.687%   $154.9158   $154.92   $154.90   $154.90  
  Purchase #4 $156.88   5.172%   $164.9938   $164.99   $165.00   $165.00  
  Purchase #5 $185.90   8.396%   $201.5082   $201.51   $201.50   $201.50  
  Purchase #6 $118.80   7.371%   $127.5567   $127.56   $127.55   $127.60  
  Purchase #7 $239.90   9.113%   $261.7621   $261.76   $261.75   $261.80  
  7 purchase totals = $1,094.82       $1,174.2536   $1,174.25   $1,174.20   $1,174.30