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 $53.33   6.469%   $56.7799   $56.78   $56.80   $56.80  
  Purchase #2 $119.94   5.809%   $126.9073   $126.91   $126.90   $126.90  
  Purchase #3 $197.38   5.199%   $207.6418   $207.64   $207.65   $207.60  
  Purchase #4 $136.92   4.662%   $143.3032   $143.30   $143.30   $143.30  
  Purchase #5 $48.42   12.631%   $54.5359   $54.54   $54.55   $54.50  
  Purchase #6 $234.59   11.798%   $262.2669   $262.27   $262.25   $262.30  
  Purchase #7 $82.71   4.481%   $86.4162   $86.42   $86.40   $86.40  
  7 purchase totals = $873.29       $937.8512   $937.86   $937.85   $937.80