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 $76.58   12.352%   $86.0392   $86.04   $86.05   $86.00  
  Purchase #2 $80.49   4.330%   $83.9752   $83.98   $84.00   $84.00  
  Purchase #3 $218.55   5.175%   $229.86   $229.86   $229.85   $229.90  
  Purchase #4 $80.69   13.326%   $91.4427   $91.44   $91.45   $91.40  
  Purchase #5 $148.70   9.793%   $163.2622   $163.26   $163.25   $163.30  
  Purchase #6 $82.44   12.622%   $92.8456   $92.85   $92.85   $92.80  
  Purchase #7 $139.38   11.298%   $155.1272   $155.13   $155.15   $155.10  
  7 purchase totals = $826.83       $902.5521   $902.56   $902.60   $902.50