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 $198.92   13.840%   $226.4505   $226.45   $226.45   $226.50  
  Purchase #2 $224.79   3.497%   $232.6509   $232.65   $232.65   $232.70  
  Purchase #3 $168.95   5.277%   $177.8655   $177.87   $177.85   $177.90  
  Purchase #4 $81.57   6.441%   $86.8239   $86.82   $86.80   $86.80  
  Purchase #5 $194.26   11.103%   $215.8287   $215.83   $215.85   $215.80  
  Purchase #6 $216.55   10.760%   $239.8508   $239.85   $239.85   $239.90  
  Purchase #7 $235.69   8.705%   $256.2068   $256.21   $256.20   $256.20  
  7 purchase totals = $1,320.73       $1,435.6771   $1,435.68   $1,435.65   $1,435.80