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 $149.43   8.646%   $162.3497   $162.35   $162.35   $162.30  
  Purchase #2 $193.87   12.204%   $217.5299   $217.53   $217.55   $217.50  
  Purchase #3 $214.37   10.359%   $236.5766   $236.58   $236.60   $236.60  
  Purchase #4 $206.64   11.519%   $230.4429   $230.44   $230.45   $230.40  
  Purchase #5 $94.70   12.745%   $106.7695   $106.77   $106.75   $106.80  
  Purchase #6 $141.60   5.151%   $148.8938   $148.89   $148.90   $148.90  
  Purchase #7 $248.81   4.758%   $260.6484   $260.65   $260.65   $260.60  
  7 purchase totals = $1,249.42       $1,363.2108   $1,363.21   $1,363.25   $1,363.10