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 $222.61   13.639%   $252.9718   $252.97   $252.95   $253.00  
  Purchase #2 $165.77   4.763%   $173.6656   $173.67   $173.65   $173.70  
  Purchase #3 $37.34   8.577%   $40.5427   $40.54   $40.55   $40.50  
  Purchase #4 $191.29   7.456%   $205.5526   $205.55   $205.55   $205.60  
  Purchase #5 $38.55   11.843%   $43.1155   $43.12   $43.10   $43.10  
  Purchase #6 $47.38   4.608%   $49.5633   $49.56   $49.55   $49.60  
  Purchase #7 $116.25   6.626%   $123.9527   $123.95   $123.95   $124.00  
  7 purchase totals = $819.19       $889.3642   $889.36   $889.30   $889.50