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 $58.77   3.269%   $60.6912   $60.69   $60.70   $60.70  
  Purchase #2 $52.67   4.273%   $54.9206   $54.92   $54.90   $54.90  
  Purchase #3 $237.29   8.538%   $257.5498   $257.55   $257.55   $257.50  
  Purchase #4 $80.97   6.744%   $86.4306   $86.43   $86.45   $86.40  
  Purchase #5 $76.83   9.354%   $84.0167   $84.02   $84.00   $84.00  
  Purchase #6 $154.82   4.441%   $161.6956   $161.70   $161.70   $161.70  
  Purchase #7 $183.59   8.444%   $199.0923   $199.09   $199.10   $199.10  
  7 purchase totals = $844.94       $904.3968   $904.40   $904.40   $904.30