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 $83.70   13.713%   $95.1778   $95.18   $95.20   $95.20  
  Purchase #2 $21.56   9.566%   $23.6224   $23.62   $23.60   $23.60  
  Purchase #3 $42.68   3.800%   $44.3018   $44.30   $44.30   $44.30  
  Purchase #4 $230.39   7.752%   $248.2498   $248.25   $248.25   $248.20  
  Purchase #5 $139.30   6.249%   $148.0049   $148.00   $148.00   $148.00  
  Purchase #6 $201.25   5.605%   $212.5301   $212.53   $212.55   $212.50  
  Purchase #7 $15.51   5.765%   $16.4042   $16.40   $16.40   $16.40  
  7 purchase totals = $734.39       $788.2910   $788.28   $788.30   $788.20