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 $250.61   4.492%   $261.8674   $261.87   $261.85   $261.90  
  Purchase #2 $181.31   6.180%   $192.515   $192.52   $192.50   $192.50  
  Purchase #3 $78.95   3.530%   $81.7369   $81.74   $81.75   $81.70  
  Purchase #4 $131.38   5.781%   $138.9751   $138.98   $139.00   $139.00  
  Purchase #5 $239.91   9.675%   $263.1213   $263.12   $263.10   $263.10  
  Purchase #6 $43.45   6.207%   $46.1469   $46.15   $46.15   $46.10  
  Purchase #7 $201.61   3.411%   $208.4869   $208.49   $208.50   $208.50  
  7 purchase totals = $1,127.22       $1,192.8495   $1,192.87   $1,192.85   $1,192.80