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 $94.55   3.734%   $98.0805   $98.08   $98.10   $98.10  
  Purchase #2 $171.25   3.149%   $176.6427   $176.64   $176.65   $176.60  
  Purchase #3 $193.81   7.242%   $207.8457   $207.85   $207.85   $207.80  
  Purchase #4 $23.85   12.116%   $26.7397   $26.74   $26.75   $26.70  
  Purchase #5 $127.58   11.701%   $142.5081   $142.51   $142.50   $142.50  
  Purchase #6 $202.86   4.849%   $212.6967   $212.70   $212.70   $212.70  
  Purchase #7 $79.62   7.193%   $85.3471   $85.35   $85.35   $85.30  
  7 purchase totals = $893.52       $949.8605   $949.87   $949.90   $949.70