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 $68.90   6.737%   $73.5418   $73.54   $73.55   $73.50  
  Purchase #2 $134.89   6.698%   $143.9249   $143.92   $143.90   $143.90  
  Purchase #3 $243.48   3.392%   $251.7388   $251.74   $251.75   $251.70  
  Purchase #4 $90.99   8.392%   $98.6259   $98.63   $98.65   $98.60  
  Purchase #5 $111.84   7.423%   $120.1419   $120.14   $120.15   $120.10  
  Purchase #6 $163.28   7.716%   $175.8787   $175.88   $175.90   $175.90  
  Purchase #7 $241.32   13.504%   $273.9079   $273.91   $273.90   $273.90  
  7 purchase totals = $1,054.70       $1,137.7599   $1,137.76   $1,137.80   $1,137.60