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 $208.38   12.408%   $234.2358   $234.24   $234.25   $234.20  
  Purchase #2 $10.71   5.804%   $11.3316   $11.33   $11.35   $11.30  
  Purchase #3 $51.60   13.805%   $58.7234   $58.72   $58.70   $58.70  
  Purchase #4 $123.83   5.224%   $130.2989   $130.30   $130.30   $130.30  
  Purchase #5 $205.57   7.802%   $221.6086   $221.61   $221.60   $221.60  
  Purchase #6 $124.83   3.735%   $129.4924   $129.49   $129.50   $129.50  
  Purchase #7 $60.50   11.712%   $67.5858   $67.59   $67.60   $67.60  
  7 purchase totals = $785.42       $853.2765   $853.28   $853.30   $853.20