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 $244.59   10.262%   $269.6898   $269.69   $269.70   $269.70  
  Purchase #2 $224.32   11.237%   $249.5268   $249.53   $249.55   $249.50  
  Purchase #3 $47.89   4.834%   $50.205   $50.21   $50.20   $50.20  
  Purchase #4 $240.55   12.578%   $270.8064   $270.81   $270.80   $270.80  
  Purchase #5 $250.26   11.414%   $278.8247   $278.82   $278.80   $278.80  
  Purchase #6 $134.99   7.298%   $144.8416   $144.84   $144.85   $144.80  
  Purchase #7 $11.32   5.632%   $11.9575   $11.96   $11.95   $12.00  
  7 purchase totals = $1,153.92       $1,275.8518   $1,275.86   $1,275.85   $1,275.80