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 $114.29   7.748%   $123.1452   $123.15   $123.15   $123.10  
  Purchase #2 $11.81   13.137%   $13.3615   $13.36   $13.35   $13.40  
  Purchase #3 $167.67   9.577%   $183.7278   $183.73   $183.75   $183.70  
  Purchase #4 $164.73   6.631%   $175.6532   $175.65   $175.65   $175.70  
  Purchase #5 $127.55   6.577%   $135.939   $135.94   $135.95   $135.90  
  Purchase #6 $101.58   5.652%   $107.3213   $107.32   $107.30   $107.30  
  Purchase #7 $78.80   8.537%   $85.5272   $85.53   $85.55   $85.50  
  7 purchase totals = $766.43       $824.6752   $824.68   $824.70   $824.60