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 $227.44   13.767%   $258.7517   $258.75   $258.75   $258.80  
  Purchase #2 $215.99   6.322%   $229.6449   $229.64   $229.65   $229.60  
  Purchase #3 $241.75   10.663%   $267.5278   $267.53   $267.55   $267.50  
  Purchase #4 $53.44   8.381%   $57.9188   $57.92   $57.90   $57.90  
  Purchase #5 $12.86   11.364%   $14.3214   $14.32   $14.30   $14.30  
  Purchase #6 $194.28   5.768%   $205.4861   $205.49   $205.50   $205.50  
  Purchase #7 $194.67   8.758%   $211.7192   $211.72   $211.70   $211.70  
  7 purchase totals = $1,140.43       $1,245.3699   $1,245.37   $1,245.35   $1,245.30