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 $118.48   13.666%   $134.6715   $134.67   $134.65   $134.70  
  Purchase #2 $128.73   4.115%   $134.0272   $134.03   $134.05   $134.00  
  Purchase #3 $69.72   11.643%   $77.8375   $77.84   $77.85   $77.80  
  Purchase #4 $182.91   6.795%   $195.3387   $195.34   $195.35   $195.30  
  Purchase #5 $168.37   10.798%   $186.5506   $186.55   $186.55   $186.60  
  Purchase #6 $103.95   3.794%   $107.8939   $107.89   $107.90   $107.90  
  Purchase #7 $210.91   11.655%   $235.4916   $235.49   $235.50   $235.50  
  7 purchase totals = $983.07       $1,071.8110   $1,071.81   $1,071.85   $1,071.80