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 $22.88   13.471%   $25.9622   $25.96   $25.95   $26.00  
  Purchase #2 $208.64   6.289%   $221.7614   $221.76   $221.75   $221.80  
  Purchase #3 $81.55   3.584%   $84.4728   $84.47   $84.45   $84.50  
  Purchase #4 $228.88   5.252%   $240.9008   $240.90   $240.90   $240.90  
  Purchase #5 $200.29   4.483%   $209.269   $209.27   $209.25   $209.30  
  Purchase #6 $31.99   6.292%   $34.0028   $34.00   $34.00   $34.00  
  Purchase #7 $67.49   11.291%   $75.1103   $75.11   $75.10   $75.10  
  7 purchase totals = $841.72       $891.4793   $891.47   $891.40   $891.60