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 $248.72   8.259%   $269.2618   $269.26   $269.25   $269.30  
  Purchase #2 $40.84   13.109%   $46.1937   $46.19   $46.20   $46.20  
  Purchase #3 $25.64   3.149%   $26.4474   $26.45   $26.45   $26.40  
  Purchase #4 $153.33   5.127%   $161.1912   $161.19   $161.20   $161.20  
  Purchase #5 $185.86   3.405%   $192.1885   $192.19   $192.20   $192.20  
  Purchase #6 $156.68   11.385%   $174.518   $174.52   $174.50   $174.50  
  Purchase #7 $21.50   7.754%   $23.1671   $23.17   $23.15   $23.20  
  7 purchase totals = $832.57       $892.9677   $892.97   $892.95   $893.00