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 $32.76   9.342%   $35.8204   $35.82   $35.80   $35.80  
  Purchase #2 $80.44   7.597%   $86.551   $86.55   $86.55   $86.60  
  Purchase #3 $110.87   3.639%   $114.9046   $114.90   $114.90   $114.90  
  Purchase #4 $107.47   11.129%   $119.4303   $119.43   $119.45   $119.40  
  Purchase #5 $98.95   8.511%   $107.3716   $107.37   $107.35   $107.40  
  Purchase #6 $192.97   10.211%   $212.6742   $212.67   $212.65   $212.70  
  Purchase #7 $208.72   4.301%   $217.697   $217.70   $217.70   $217.70  
  7 purchase totals = $832.18       $894.4491   $894.44   $894.40   $894.50