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 $148.82   4.291%   $155.2059   $155.21   $155.20   $155.20  
  Purchase #2 $242.48   9.699%   $265.9981   $266.00   $266.00   $266.00  
  Purchase #3 $208.71   8.614%   $226.6883   $226.69   $226.70   $226.70  
  Purchase #4 $175.50   3.302%   $181.295   $181.30   $181.30   $181.30  
  Purchase #5 $82.66   5.836%   $87.484   $87.48   $87.50   $87.50  
  Purchase #6 $77.53   11.282%   $86.2769   $86.28   $86.30   $86.30  
  Purchase #7 $92.89   12.813%   $104.792   $104.79   $104.80   $104.80  
  7 purchase totals = $1,028.59       $1,107.7402   $1,107.75   $1,107.80   $1,107.80