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 $61.76   3.704%   $64.0476   $64.05   $64.05   $64.00  
  Purchase #2 $188.96   6.104%   $200.4941   $200.49   $200.50   $200.50  
  Purchase #3 $121.83   5.129%   $128.0787   $128.08   $128.10   $128.10  
  Purchase #4 $174.53   6.798%   $186.3945   $186.39   $186.40   $186.40  
  Purchase #5 $181.92   3.225%   $187.7869   $187.79   $187.80   $187.80  
  Purchase #6 $17.68   3.611%   $18.3184   $18.32   $18.30   $18.30  
  Purchase #7 $125.41   6.793%   $133.9291   $133.93   $133.95   $133.90  
  7 purchase totals = $872.09       $919.0493   $919.05   $919.10   $919.00