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 $40.96   8.724%   $44.5334   $44.53   $44.55   $44.50  
  Purchase #2 $118.93   5.310%   $125.2452   $125.25   $125.25   $125.20  
  Purchase #3 $148.99   3.289%   $153.8903   $153.89   $153.90   $153.90  
  Purchase #4 $81.43   11.440%   $90.7456   $90.75   $90.75   $90.70  
  Purchase #5 $201.65   12.521%   $226.8986   $226.90   $226.90   $226.90  
  Purchase #6 $206.63   4.424%   $215.7713   $215.77   $215.75   $215.80  
  Purchase #7 $86.29   13.636%   $98.0565   $98.06   $98.05   $98.10  
  7 purchase totals = $884.88       $955.1409   $955.15   $955.15   $955.10