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 $41.89   13.534%   $47.5594   $47.56   $47.55   $47.60  
  Purchase #2 $100.29   13.284%   $113.6125   $113.61   $113.60   $113.60  
  Purchase #3 $250.91   12.505%   $282.2863   $282.29   $282.30   $282.30  
  Purchase #4 $125.81   10.741%   $139.3233   $139.32   $139.30   $139.30  
  Purchase #5 $216.94   8.115%   $234.5447   $234.54   $234.55   $234.50  
  Purchase #6 $156.64   8.299%   $169.6396   $169.64   $169.65   $169.60  
  Purchase #7 $220.59   12.440%   $248.0314   $248.03   $248.05   $248.00  
  7 purchase totals = $1,113.07       $1,234.9972   $1,234.99   $1,235.00   $1,234.90