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 $232.85   8.441%   $252.5049   $252.50   $252.50   $252.50  
  Purchase #2 $146.51   7.804%   $157.9436   $157.94   $157.95   $157.90  
  Purchase #3 $56.53   9.773%   $62.0547   $62.05   $62.05   $62.10  
  Purchase #4 $209.38   9.763%   $229.8218   $229.82   $229.80   $229.80  
  Purchase #5 $191.28   8.829%   $208.1681   $208.17   $208.15   $208.20  
  Purchase #6 $116.53   10.451%   $128.7086   $128.71   $128.70   $128.70  
  Purchase #7 $63.89   6.248%   $67.8818   $67.88   $67.90   $67.90  
  7 purchase totals = $1,016.97       $1,107.0835   $1,107.07   $1,107.05   $1,107.10