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 $249.38   6.529%   $265.662   $265.66   $265.65   $265.70  
  Purchase #2 $121.62   10.696%   $134.6285   $134.63   $134.65   $134.60  
  Purchase #3 $91.45   9.291%   $99.9466   $99.95   $99.95   $99.90  
  Purchase #4 $67.60   12.494%   $76.0459   $76.05   $76.05   $76.00  
  Purchase #5 $192.53   7.603%   $207.1681   $207.17   $207.15   $207.20  
  Purchase #6 $161.75   4.805%   $169.5221   $169.52   $169.50   $169.50  
  Purchase #7 $12.90   4.602%   $13.4937   $13.49   $13.50   $13.50  
  7 purchase totals = $897.23       $966.4669   $966.47   $966.45   $966.40