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 $161.87   13.381%   $183.5298   $183.53   $183.55   $183.50  
  Purchase #2 $232.27   6.156%   $246.5685   $246.57   $246.55   $246.60  
  Purchase #3 $180.56   9.707%   $198.087   $198.09   $198.10   $198.10  
  Purchase #4 $207.26   3.478%   $214.4685   $214.47   $214.45   $214.50  
  Purchase #5 $146.70   8.815%   $159.6316   $159.63   $159.65   $159.60  
  Purchase #6 $146.61   3.277%   $151.4144   $151.41   $151.40   $151.40  
  Purchase #7 $171.47   5.622%   $181.11   $181.11   $181.10   $181.10  
  7 purchase totals = $1,246.74       $1,334.8098   $1,334.81   $1,334.80   $1,334.80