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 $61.76   13.326%   $69.9901   $69.99   $70.00   $70.00  
  Purchase #2 $81.69   9.556%   $89.4963   $89.50   $89.50   $89.50  
  Purchase #3 $113.67   4.867%   $119.2023   $119.20   $119.20   $119.20  
  Purchase #4 $69.43   10.735%   $76.8833   $76.88   $76.90   $76.90  
  Purchase #5 $232.83   8.224%   $251.9779   $251.98   $252.00   $252.00  
  Purchase #6 $211.79   9.650%   $232.2277   $232.23   $232.25   $232.20  
  Purchase #7 $188.66   12.410%   $212.0727   $212.07   $212.05   $212.10  
  7 purchase totals = $959.83       $1,051.8503   $1,051.85   $1,051.90   $1,051.90