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 $206.28   13.247%   $233.6059   $233.61   $233.60   $233.60  
  Purchase #2 $133.29   10.774%   $147.6507   $147.65   $147.65   $147.70  
  Purchase #3 $86.62   12.542%   $97.4839   $97.48   $97.50   $97.50  
  Purchase #4 $118.28   9.845%   $129.9247   $129.92   $129.90   $129.90  
  Purchase #5 $114.70   3.242%   $118.4186   $118.42   $118.40   $118.40  
  Purchase #6 $82.78   3.693%   $85.8371   $85.84   $85.85   $85.80  
  Purchase #7 $165.33   6.872%   $176.6915   $176.69   $176.70   $176.70  
  7 purchase totals = $907.28       $989.6124   $989.61   $989.60   $989.60