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 $154.71   7.520%   $166.3442   $166.34   $166.35   $166.30  
  Purchase #2 $232.89   6.618%   $248.3027   $248.30   $248.30   $248.30  
  Purchase #3 $51.82   8.788%   $56.3739   $56.37   $56.35   $56.40  
  Purchase #4 $212.66   4.848%   $222.9698   $222.97   $222.95   $223.00  
  Purchase #5 $250.41   9.416%   $273.9886   $273.99   $274.00   $274.00  
  Purchase #6 $69.97   4.525%   $73.1361   $73.14   $73.15   $73.10  
  Purchase #7 $213.87   5.123%   $224.8266   $224.83   $224.85   $224.80  
  7 purchase totals = $1,186.33       $1,265.9419   $1,265.94   $1,265.95   $1,265.90