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 $250.52   6.708%   $267.3249   $267.32   $267.30   $267.30  
  Purchase #2 $109.59   9.204%   $119.6767   $119.68   $119.70   $119.70  
  Purchase #3 $162.56   3.846%   $168.8121   $168.81   $168.80   $168.80  
  Purchase #4 $77.80   11.295%   $86.5875   $86.59   $86.60   $86.60  
  Purchase #5 $109.95   5.125%   $115.5849   $115.58   $115.60   $115.60  
  Purchase #6 $240.67   3.323%   $248.6675   $248.67   $248.65   $248.70  
  Purchase #7 $191.99   7.691%   $206.756   $206.76   $206.75   $206.80  
  7 purchase totals = $1,143.08       $1,213.4096   $1,213.41   $1,213.40   $1,213.50