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 $208.83   13.798%   $237.6444   $237.64   $237.65   $237.60  
  Purchase #2 $154.45   8.144%   $167.0284   $167.03   $167.05   $167.00  
  Purchase #3 $122.34   3.253%   $126.3197   $126.32   $126.30   $126.30  
  Purchase #4 $183.99   12.629%   $207.2261   $207.23   $207.25   $207.20  
  Purchase #5 $230.28   12.519%   $259.1088   $259.11   $259.10   $259.10  
  Purchase #6 $108.84   3.307%   $112.4393   $112.44   $112.45   $112.40  
  Purchase #7 $48.30   3.358%   $49.9219   $49.92   $49.90   $49.90  
  7 purchase totals = $1,057.03       $1,159.6886   $1,159.69   $1,159.70   $1,159.50