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 $224.71   7.596%   $241.779   $241.78   $241.80   $241.80  
  Purchase #2 $48.54   7.357%   $52.1111   $52.11   $52.10   $52.10  
  Purchase #3 $146.82   10.212%   $161.8133   $161.81   $161.80   $161.80  
  Purchase #4 $100.50   13.597%   $114.165   $114.17   $114.15   $114.20  
  Purchase #5 $81.37   6.699%   $86.821   $86.82   $86.80   $86.80  
  Purchase #6 $94.62   11.684%   $105.6754   $105.68   $105.70   $105.70  
  Purchase #7 $230.85   12.837%   $260.4842   $260.48   $260.50   $260.50  
  7 purchase totals = $927.41       $1,022.8490   $1,022.85   $1,022.85   $1,022.90