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 $225.49   11.744%   $251.9715   $251.97   $251.95   $252.00  
  Purchase #2 $165.83   10.306%   $182.9204   $182.92   $182.90   $182.90  
  Purchase #3 $60.27   4.120%   $62.7531   $62.75   $62.75   $62.80  
  Purchase #4 $235.30   5.456%   $248.138   $248.14   $248.15   $248.10  
  Purchase #5 $12.93   3.782%   $13.419   $13.42   $13.40   $13.40  
  Purchase #6 $41.91   4.337%   $43.7276   $43.73   $43.75   $43.70  
  Purchase #7 $148.30   8.826%   $161.389   $161.39   $161.40   $161.40  
  7 purchase totals = $890.03       $964.3186   $964.32   $964.30   $964.30