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 $42.99   8.615%   $46.6936   $46.69   $46.70   $46.70  
  Purchase #2 $242.39   6.225%   $257.4788   $257.48   $257.50   $257.50  
  Purchase #3 $244.51   8.799%   $266.0244   $266.02   $266.00   $266.00  
  Purchase #4 $14.49   7.550%   $15.584   $15.58   $15.60   $15.60  
  Purchase #5 $70.93   8.640%   $77.0584   $77.06   $77.05   $77.10  
  Purchase #6 $179.89   6.839%   $192.1927   $192.19   $192.20   $192.20  
  Purchase #7 $49.49   8.340%   $53.6175   $53.62   $53.60   $53.60  
  7 purchase totals = $844.69       $908.6494   $908.64   $908.65   $908.70