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 $58.74   13.493%   $66.6658   $66.67   $66.65   $66.70  
  Purchase #2 $226.96   4.632%   $237.4728   $237.47   $237.45   $237.50  
  Purchase #3 $53.52   12.614%   $60.271   $60.27   $60.25   $60.30  
  Purchase #4 $47.50   6.684%   $50.6749   $50.67   $50.65   $50.70  
  Purchase #5 $106.40   7.748%   $114.6439   $114.64   $114.65   $114.60  
  Purchase #6 $49.56   12.292%   $55.6519   $55.65   $55.65   $55.70  
  Purchase #7 $62.41   6.376%   $66.3893   $66.39   $66.40   $66.40  
  7 purchase totals = $605.09       $651.7696   $651.76   $651.70   $651.90