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 $58.93   10.284%   $64.9904   $64.99   $65.00   $65.00  
  Purchase #2 $114.48   8.632%   $124.3619   $124.36   $124.35   $124.40  
  Purchase #3 $13.52   12.798%   $15.2503   $15.25   $15.25   $15.30  
  Purchase #4 $186.51   8.620%   $202.5872   $202.59   $202.60   $202.60  
  Purchase #5 $151.94   10.181%   $167.409   $167.41   $167.40   $167.40  
  Purchase #6 $25.68   8.695%   $27.9129   $27.91   $27.90   $27.90  
  Purchase #7 $70.96   7.669%   $76.4019   $76.40   $76.40   $76.40  
  7 purchase totals = $622.02       $678.9136   $678.91   $678.90   $679.00