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 $51.43   13.255%   $58.247   $58.25   $58.25   $58.20  
  Purchase #2 $164.79   11.114%   $183.1048   $183.10   $183.10   $183.10  
  Purchase #3 $145.55   13.771%   $165.5937   $165.59   $165.60   $165.60  
  Purchase #4 $169.67   8.440%   $183.9901   $183.99   $184.00   $184.00  
  Purchase #5 $165.63   3.212%   $170.95   $170.95   $170.95   $171.00  
  Purchase #6 $18.68   3.127%   $19.2641   $19.26   $19.25   $19.30  
  Purchase #7 $208.88   11.129%   $232.1263   $232.13   $232.15   $232.10  
  7 purchase totals = $924.63       $1,013.2760   $1,013.27   $1,013.30   $1,013.30