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 $46.43   11.333%   $51.6919   $51.69   $51.70   $51.70  
  Purchase #2 $226.79   4.195%   $236.3038   $236.30   $236.30   $236.30  
  Purchase #3 $115.26   12.516%   $129.6859   $129.69   $129.70   $129.70  
  Purchase #4 $78.44   10.348%   $86.557   $86.56   $86.55   $86.60  
  Purchase #5 $144.60   4.447%   $151.0304   $151.03   $151.05   $151.00  
  Purchase #6 $137.82   13.781%   $156.813   $156.81   $156.80   $156.80  
  Purchase #7 $239.83   4.287%   $250.1115   $250.11   $250.10   $250.10  
  7 purchase totals = $989.17       $1,062.1935   $1,062.19   $1,062.20   $1,062.20