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 $84.34   8.772%   $91.7383   $91.74   $91.75   $91.70  
  Purchase #2 $219.81   3.107%   $226.6395   $226.64   $226.65   $226.60  
  Purchase #3 $240.55   5.409%   $253.5613   $253.56   $253.55   $253.60  
  Purchase #4 $161.80   6.187%   $171.8106   $171.81   $171.80   $171.80  
  Purchase #5 $186.69   3.597%   $193.4052   $193.41   $193.40   $193.40  
  Purchase #6 $242.30   10.536%   $267.8287   $267.83   $267.85   $267.80  
  Purchase #7 $237.42   10.175%   $261.5775   $261.58   $261.60   $261.60  
  7 purchase totals = $1,372.91       $1,466.5611   $1,466.57   $1,466.60   $1,466.50