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 $156.47   11.789%   $174.9162   $174.92   $174.90   $174.90  
  Purchase #2 $237.68   12.411%   $267.1785   $267.18   $267.20   $267.20  
  Purchase #3 $189.31   10.169%   $208.5609   $208.56   $208.55   $208.60  
  Purchase #4 $83.70   3.564%   $86.6831   $86.68   $86.70   $86.70  
  Purchase #5 $52.67   9.554%   $57.7021   $57.70   $57.70   $57.70  
  Purchase #6 $88.44   13.798%   $100.643   $100.64   $100.65   $100.60  
  Purchase #7 $163.89   7.525%   $176.2227   $176.22   $176.20   $176.20  
  7 purchase totals = $972.16       $1,071.9065   $1,071.90   $1,071.90   $1,071.90