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 $228.37   13.262%   $258.6564   $258.66   $258.65   $258.70  
  Purchase #2 $226.77   6.493%   $241.4942   $241.49   $241.50   $241.50  
  Purchase #3 $10.73   13.691%   $12.199   $12.20   $12.20   $12.20  
  Purchase #4 $134.25   3.640%   $139.1367   $139.14   $139.15   $139.10  
  Purchase #5 $168.76   12.462%   $189.7909   $189.79   $189.80   $189.80  
  Purchase #6 $119.56   4.662%   $125.1339   $125.13   $125.15   $125.10  
  Purchase #7 $57.81   4.388%   $60.3467   $60.35   $60.35   $60.30  
  7 purchase totals = $946.25       $1,026.7578   $1,026.76   $1,026.80   $1,026.70