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 $59.54   7.382%   $63.9352   $63.94   $63.95   $63.90  
  Purchase #2 $159.83   9.371%   $174.8077   $174.81   $174.80   $174.80  
  Purchase #3 $177.68   6.740%   $189.6556   $189.66   $189.65   $189.70  
  Purchase #4 $235.91   5.554%   $249.0124   $249.01   $249.00   $249.00  
  Purchase #5 $163.82   7.820%   $176.6307   $176.63   $176.65   $176.60  
  Purchase #6 $230.70   11.439%   $257.0898   $257.09   $257.10   $257.10  
  Purchase #7 $36.99   4.102%   $38.5073   $38.51   $38.50   $38.50  
  7 purchase totals = $1,064.47       $1,149.6387   $1,149.65   $1,149.65   $1,149.60