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 $103.63   13.466%   $117.5848   $117.58   $117.60   $117.60  
  Purchase #2 $219.53   10.236%   $242.0011   $242.00   $242.00   $242.00  
  Purchase #3 $120.91   6.195%   $128.4004   $128.40   $128.40   $128.40  
  Purchase #4 $51.64   8.560%   $56.0604   $56.06   $56.05   $56.10  
  Purchase #5 $212.81   13.396%   $241.318   $241.32   $241.30   $241.30  
  Purchase #6 $231.59   12.694%   $260.988   $260.99   $261.00   $261.00  
  Purchase #7 $217.55   10.418%   $240.2144   $240.21   $240.20   $240.20  
  7 purchase totals = $1,157.66       $1,286.5671   $1,286.56   $1,286.55   $1,286.60