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 $231.50   9.516%   $253.5295   $253.53   $253.55   $253.50  
  Purchase #2 $107.62   6.488%   $114.6024   $114.60   $114.60   $114.60  
  Purchase #3 $42.85   9.725%   $47.0172   $47.02   $47.00   $47.00  
  Purchase #4 $196.78   12.443%   $221.2653   $221.27   $221.25   $221.30  
  Purchase #5 $126.39   6.279%   $134.326   $134.33   $134.35   $134.30  
  Purchase #6 $57.49   7.648%   $61.8868   $61.89   $61.90   $61.90  
  Purchase #7 $208.92   7.592%   $224.7812   $224.78   $224.80   $224.80  
  7 purchase totals = $971.55       $1,057.4084   $1,057.42   $1,057.45   $1,057.40