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 $61.66   11.203%   $68.5678   $68.57   $68.55   $68.60  
  Purchase #2 $92.46   5.739%   $97.7663   $97.77   $97.75   $97.80  
  Purchase #3 $29.71   12.752%   $33.4986   $33.50   $33.50   $33.50  
  Purchase #4 $234.26   11.629%   $261.5021   $261.50   $261.50   $261.50  
  Purchase #5 $64.79   3.703%   $67.1892   $67.19   $67.20   $67.20  
  Purchase #6 $101.81   9.710%   $111.6958   $111.70   $111.70   $111.70  
  Purchase #7 $234.48   12.513%   $263.8205   $263.82   $263.80   $263.80  
  7 purchase totals = $819.17       $904.0403   $904.05   $904.00   $904.10