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 $83.50   12.423%   $93.8732   $93.87   $93.85   $93.90  
  Purchase #2 $160.90   10.266%   $177.418   $177.42   $177.40   $177.40  
  Purchase #3 $53.38   11.577%   $59.5598   $59.56   $59.55   $59.60  
  Purchase #4 $14.91   8.152%   $16.1255   $16.13   $16.15   $16.10  
  Purchase #5 $191.62   8.203%   $207.3386   $207.34   $207.35   $207.30  
  Purchase #6 $90.95   11.547%   $101.452   $101.45   $101.45   $101.50  
  Purchase #7 $183.94   13.185%   $208.1925   $208.19   $208.20   $208.20  
  7 purchase totals = $779.20       $863.9596   $863.96   $863.95   $864.00