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 $47.43   11.845%   $53.0481   $53.05   $53.05   $53.00  
  Purchase #2 $248.45   4.245%   $258.9967   $259.00   $259.00   $259.00  
  Purchase #3 $53.26   12.447%   $59.8893   $59.89   $59.90   $59.90  
  Purchase #4 $118.92   3.279%   $122.8194   $122.82   $122.80   $122.80  
  Purchase #5 $89.49   7.432%   $96.1409   $96.14   $96.15   $96.10  
  Purchase #6 $248.93   11.770%   $278.2291   $278.23   $278.25   $278.20  
  Purchase #7 $150.89   5.476%   $159.1527   $159.15   $159.15   $159.20  
  7 purchase totals = $957.37       $1,028.2762   $1,028.28   $1,028.30   $1,028.20