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 $113.47   10.537%   $125.4263   $125.43   $125.45   $125.40  
  Purchase #2 $192.60   3.795%   $199.9092   $199.91   $199.90   $199.90  
  Purchase #3 $105.95   7.714%   $114.123   $114.12   $114.10   $114.10  
  Purchase #4 $231.26   3.739%   $239.9068   $239.91   $239.90   $239.90  
  Purchase #5 $112.77   9.668%   $123.6726   $123.67   $123.65   $123.70  
  Purchase #6 $227.42   8.417%   $246.5619   $246.56   $246.55   $246.60  
  Purchase #7 $16.49   11.279%   $18.3499   $18.35   $18.35   $18.30  
  7 purchase totals = $999.96       $1,067.9497   $1,067.95   $1,067.90   $1,067.90