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 $209.90   12.399%   $235.9255   $235.93   $235.95   $235.90  
  Purchase #2 $146.35   5.669%   $154.6466   $154.65   $154.65   $154.60  
  Purchase #3 $49.55   3.227%   $51.149   $51.15   $51.15   $51.10  
  Purchase #4 $48.99   12.316%   $55.0236   $55.02   $55.00   $55.00  
  Purchase #5 $41.47   11.365%   $46.1831   $46.18   $46.20   $46.20  
  Purchase #6 $162.86   6.284%   $173.0941   $173.09   $173.10   $173.10  
  Purchase #7 $218.41   13.655%   $248.2339   $248.23   $248.25   $248.20  
  7 purchase totals = $877.53       $964.2558   $964.25   $964.30   $964.10