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 $227.88   3.398%   $235.6234   $235.62   $235.60   $235.60  
  Purchase #2 $216.26   9.794%   $237.4405   $237.44   $237.45   $237.40  
  Purchase #3 $112.54   6.252%   $119.576   $119.58   $119.60   $119.60  
  Purchase #4 $59.35   6.448%   $63.1769   $63.18   $63.20   $63.20  
  Purchase #5 $49.68   3.581%   $51.459   $51.46   $51.45   $51.50  
  Purchase #6 $61.53   13.448%   $69.8046   $69.80   $69.80   $69.80  
  Purchase #7 $129.30   4.253%   $134.7991   $134.80   $134.80   $134.80  
  7 purchase totals = $856.54       $911.8795   $911.88   $911.90   $911.90