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 $115.58   3.552%   $119.6854   $119.69   $119.70   $119.70  
  Purchase #2 $150.89   6.661%   $160.9408   $160.94   $160.95   $160.90  
  Purchase #3 $10.26   12.521%   $11.5447   $11.54   $11.55   $11.50  
  Purchase #4 $43.48   7.272%   $46.6419   $46.64   $46.65   $46.60  
  Purchase #5 $225.99   12.568%   $254.3924   $254.39   $254.40   $254.40  
  Purchase #6 $233.41   4.747%   $244.49   $244.49   $244.50   $244.50  
  Purchase #7 $133.33   11.533%   $148.7069   $148.71   $148.70   $148.70  
  7 purchase totals = $912.94       $986.4021   $986.40   $986.45   $986.30