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 $12.93   10.440%   $14.2799   $14.28   $14.30   $14.30  
  Purchase #2 $181.92   13.587%   $206.6375   $206.64   $206.65   $206.60  
  Purchase #3 $241.73   4.518%   $252.6514   $252.65   $252.65   $252.70  
  Purchase #4 $160.61   6.754%   $171.4576   $171.46   $171.45   $171.50  
  Purchase #5 $34.37   13.218%   $38.913   $38.91   $38.90   $38.90  
  Purchase #6 $220.44   13.799%   $250.8585   $250.86   $250.85   $250.90  
  Purchase #7 $114.37   9.153%   $124.8383   $124.84   $124.85   $124.80  
  7 purchase totals = $966.37       $1,059.6362   $1,059.64   $1,059.65   $1,059.70