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 $234.37   10.239%   $258.3671   $258.37   $258.35   $258.40  
  Purchase #2 $175.98   9.232%   $192.2265   $192.23   $192.25   $192.20  
  Purchase #3 $111.96   7.412%   $120.2585   $120.26   $120.25   $120.30  
  Purchase #4 $248.64   7.484%   $267.2482   $267.25   $267.25   $267.20  
  Purchase #5 $169.48   9.679%   $185.884   $185.88   $185.90   $185.90  
  Purchase #6 $91.87   7.241%   $98.5223   $98.52   $98.50   $98.50  
  Purchase #7 $69.63   9.457%   $76.2149   $76.21   $76.20   $76.20  
  7 purchase totals = $1,101.93       $1,198.7215   $1,198.72   $1,198.70   $1,198.70