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 $114.39   9.602%   $125.3737   $125.37   $125.35   $125.40  
  Purchase #2 $169.55   3.788%   $175.9726   $175.97   $175.95   $176.00  
  Purchase #3 $172.51   6.767%   $184.1838   $184.18   $184.20   $184.20  
  Purchase #4 $248.71   11.550%   $277.436   $277.44   $277.45   $277.40  
  Purchase #5 $34.26   10.819%   $37.9666   $37.97   $37.95   $38.00  
  Purchase #6 $8.94   7.167%   $9.5807   $9.58   $9.60   $9.60  
  Purchase #7 $167.76   13.795%   $190.9025   $190.90   $190.90   $190.90  
  7 purchase totals = $916.12       $1,001.4159   $1,001.41   $1,001.40   $1,001.50