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 $249.49   7.262%   $267.608   $267.61   $267.60   $267.60  
  Purchase #2 $118.87   7.119%   $127.3324   $127.33   $127.35   $127.30  
  Purchase #3 $47.80   3.841%   $49.636   $49.64   $49.65   $49.60  
  Purchase #4 $171.74   6.186%   $182.3638   $182.36   $182.35   $182.40  
  Purchase #5 $130.89   6.817%   $139.8128   $139.81   $139.80   $139.80  
  Purchase #6 $214.42   12.667%   $241.5806   $241.58   $241.60   $241.60  
  Purchase #7 $250.88   9.473%   $274.6459   $274.65   $274.65   $274.60  
  7 purchase totals = $1,184.09       $1,282.9795   $1,282.98   $1,283.00   $1,282.90