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 $208.45   12.811%   $235.1545   $235.15   $235.15   $235.20  
  Purchase #2 $161.64   8.344%   $175.1272   $175.13   $175.15   $175.10  
  Purchase #3 $41.71   3.179%   $43.036   $43.04   $43.05   $43.00  
  Purchase #4 $119.94   11.261%   $133.4464   $133.45   $133.45   $133.40  
  Purchase #5 $132.99   13.739%   $151.2615   $151.26   $151.25   $151.30  
  Purchase #6 $121.47   4.196%   $126.5669   $126.57   $126.55   $126.60  
  Purchase #7 $142.86   4.473%   $149.2501   $149.25   $149.25   $149.30  
  7 purchase totals = $929.06       $1,013.8426   $1,013.85   $1,013.85   $1,013.90