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 $186.29   11.763%   $208.2033   $208.20   $208.20   $208.20  
  Purchase #2 $165.97   4.484%   $173.4121   $173.41   $173.40   $173.40  
  Purchase #3 $118.26   4.246%   $123.2813   $123.28   $123.30   $123.30  
  Purchase #4 $34.52   9.300%   $37.7304   $37.73   $37.75   $37.70  
  Purchase #5 $47.95   3.657%   $49.7035   $49.70   $49.70   $49.70  
  Purchase #6 $71.29   5.738%   $75.3806   $75.38   $75.40   $75.40  
  Purchase #7 $233.64   6.317%   $248.399   $248.40   $248.40   $248.40  
  7 purchase totals = $857.92       $916.1102   $916.10   $916.15   $916.10