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 $57.78   13.507%   $65.5843   $65.58   $65.60   $65.60  
  Purchase #2 $38.68   10.738%   $42.8335   $42.83   $42.85   $42.80  
  Purchase #3 $244.27   5.386%   $257.4264   $257.43   $257.45   $257.40  
  Purchase #4 $200.61   3.584%   $207.7999   $207.80   $207.80   $207.80  
  Purchase #5 $214.42   10.311%   $236.5288   $236.53   $236.55   $236.50  
  Purchase #6 $144.90   9.164%   $158.1786   $158.18   $158.20   $158.20  
  Purchase #7 $235.77   5.805%   $249.4564   $249.46   $249.45   $249.50  
  7 purchase totals = $1,136.43       $1,217.8079   $1,217.81   $1,217.90   $1,217.80