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 $41.88   11.685%   $46.7737   $46.77   $46.75   $46.80  
  Purchase #2 $113.99   13.407%   $129.2726   $129.27   $129.25   $129.30  
  Purchase #3 $160.94   6.472%   $171.356   $171.36   $171.35   $171.40  
  Purchase #4 $163.69   7.271%   $175.5919   $175.59   $175.60   $175.60  
  Purchase #5 $235.76   12.619%   $265.5106   $265.51   $265.50   $265.50  
  Purchase #6 $132.51   8.117%   $143.2658   $143.27   $143.25   $143.30  
  Purchase #7 $109.61   4.318%   $114.343   $114.34   $114.35   $114.30  
  7 purchase totals = $958.38       $1,046.1136   $1,046.11   $1,046.05   $1,046.20