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 $42.33   11.810%   $47.3292   $47.33   $47.35   $47.30  
  Purchase #2 $241.77   8.636%   $262.6493   $262.65   $262.65   $262.60  
  Purchase #3 $214.32   12.779%   $241.708   $241.71   $241.70   $241.70  
  Purchase #4 $187.61   4.536%   $196.12   $196.12   $196.10   $196.10  
  Purchase #5 $124.57   12.416%   $140.0366   $140.04   $140.05   $140.00  
  Purchase #6 $122.35   6.692%   $130.5377   $130.54   $130.55   $130.50  
  Purchase #7 $179.76   3.460%   $185.9797   $185.98   $186.00   $186.00  
  7 purchase totals = $1,112.71       $1,204.3605   $1,204.37   $1,204.40   $1,204.20