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 $22.86   8.225%   $24.7402   $24.74   $24.75   $24.70  
  Purchase #2 $199.65   3.233%   $206.1047   $206.10   $206.10   $206.10  
  Purchase #3 $12.48   10.803%   $13.8282   $13.83   $13.85   $13.80  
  Purchase #4 $239.96   3.804%   $249.0881   $249.09   $249.10   $249.10  
  Purchase #5 $201.31   6.653%   $214.7032   $214.70   $214.70   $214.70  
  Purchase #6 $80.26   6.699%   $85.6366   $85.64   $85.65   $85.60  
  Purchase #7 $42.58   10.364%   $46.993   $46.99   $47.00   $47.00  
  7 purchase totals = $799.10       $841.0940   $841.09   $841.15   $841.00