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 $19.82   9.329%   $21.669   $21.67   $21.65   $21.70  
  Purchase #2 $191.79   12.581%   $215.9191   $215.92   $215.90   $215.90  
  Purchase #3 $240.39   10.721%   $266.1622   $266.16   $266.15   $266.20  
  Purchase #4 $186.30   12.843%   $210.2265   $210.23   $210.25   $210.20  
  Purchase #5 $176.47   8.584%   $191.6182   $191.62   $191.60   $191.60  
  Purchase #6 $35.91   8.688%   $39.0299   $39.03   $39.05   $39.00  
  Purchase #7 $180.38   13.243%   $204.2677   $204.27   $204.25   $204.30  
  7 purchase totals = $1,031.06       $1,148.8926   $1,148.90   $1,148.85   $1,148.90