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 $183.86   13.306%   $208.3244   $208.32   $208.30   $208.30  
  Purchase #2 $240.83   13.505%   $273.3541   $273.35   $273.35   $273.40  
  Purchase #3 $127.90   5.242%   $134.6045   $134.60   $134.60   $134.60  
  Purchase #4 $47.69   6.474%   $50.7775   $50.78   $50.80   $50.80  
  Purchase #5 $216.29   11.559%   $241.291   $241.29   $241.30   $241.30  
  Purchase #6 $168.60   9.259%   $184.2107   $184.21   $184.20   $184.20  
  Purchase #7 $29.53   3.484%   $30.5588   $30.56   $30.55   $30.60  
  7 purchase totals = $1,014.70       $1,123.1210   $1,123.11   $1,123.10   $1,123.20