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 $204.37   10.363%   $225.5489   $225.55   $225.55   $225.50  
  Purchase #2 $187.98   5.595%   $198.4975   $198.50   $198.50   $198.50  
  Purchase #3 $230.41   7.104%   $246.7783   $246.78   $246.80   $246.80  
  Purchase #4 $76.45   6.740%   $81.6027   $81.60   $81.60   $81.60  
  Purchase #5 $178.87   4.202%   $186.3861   $186.39   $186.40   $186.40  
  Purchase #6 $8.81   6.678%   $9.3983   $9.40   $9.40   $9.40  
  Purchase #7 $207.66   13.719%   $236.1489   $236.15   $236.15   $236.10  
  7 purchase totals = $1,094.55       $1,184.3607   $1,184.37   $1,184.40   $1,184.30