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 $235.26   9.858%   $258.4519   $258.45   $258.45   $258.50  
  Purchase #2 $110.91   11.839%   $124.0406   $124.04   $124.05   $124.00  
  Purchase #3 $32.62   3.704%   $33.8282   $33.83   $33.85   $33.80  
  Purchase #4 $222.82   13.443%   $252.7737   $252.77   $252.75   $252.80  
  Purchase #5 $152.77   8.206%   $165.3063   $165.31   $165.30   $165.30  
  Purchase #6 $8.81   8.820%   $9.587   $9.59   $9.60   $9.60  
  Purchase #7 $232.73   12.132%   $260.9648   $260.96   $260.95   $261.00  
  7 purchase totals = $995.92       $1,104.9525   $1,104.95   $1,104.95   $1,105.00