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 $56.28   9.591%   $61.6778   $61.68   $61.70   $61.70  
  Purchase #2 $65.74   11.440%   $73.2607   $73.26   $73.25   $73.30  
  Purchase #3 $64.97   10.531%   $71.812   $71.81   $71.80   $71.80  
  Purchase #4 $142.41   3.530%   $147.4371   $147.44   $147.45   $147.40  
  Purchase #5 $148.88   13.207%   $168.5426   $168.54   $168.55   $168.50  
  Purchase #6 $170.93   9.218%   $186.6863   $186.69   $186.70   $186.70  
  Purchase #7 $61.62   8.381%   $66.7844   $66.78   $66.80   $66.80  
  7 purchase totals = $710.83       $776.2009   $776.20   $776.25   $776.20