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 $69.59   11.489%   $77.5852   $77.59   $77.60   $77.60  
  Purchase #2 $228.95   11.757%   $255.8677   $255.87   $255.85   $255.90  
  Purchase #3 $53.25   8.569%   $57.813   $57.81   $57.80   $57.80  
  Purchase #4 $214.49   9.602%   $235.0853   $235.09   $235.10   $235.10  
  Purchase #5 $112.68   6.119%   $119.5749   $119.57   $119.55   $119.60  
  Purchase #6 $184.31   4.320%   $192.2722   $192.27   $192.25   $192.30  
  Purchase #7 $106.77   13.309%   $120.98   $120.98   $121.00   $121.00  
  7 purchase totals = $970.04       $1,059.1783   $1,059.18   $1,059.15   $1,059.30