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 $86.31   11.339%   $96.0967   $96.10   $96.10   $96.10  
  Purchase #2 $114.51   4.164%   $119.2782   $119.28   $119.30   $119.30  
  Purchase #3 $119.58   9.630%   $131.0956   $131.10   $131.10   $131.10  
  Purchase #4 $108.40   6.207%   $115.1284   $115.13   $115.15   $115.10  
  Purchase #5 $86.36   10.271%   $95.23   $95.23   $95.25   $95.20  
  Purchase #6 $186.65   3.171%   $192.5687   $192.57   $192.55   $192.60  
  Purchase #7 $49.68   13.815%   $56.5433   $56.54   $56.55   $56.50  
  7 purchase totals = $751.49       $805.9409   $805.95   $806.00   $805.90