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 $60.35   8.293%   $65.3548   $65.35   $65.35   $65.40  
  Purchase #2 $120.66   12.114%   $135.2768   $135.28   $135.30   $135.30  
  Purchase #3 $70.82   7.656%   $76.242   $76.24   $76.25   $76.20  
  Purchase #4 $232.42   5.750%   $245.7842   $245.78   $245.80   $245.80  
  Purchase #5 $5.49   3.711%   $5.6937   $5.69   $5.70   $5.70  
  Purchase #6 $194.76   10.782%   $215.759   $215.76   $215.75   $215.80  
  Purchase #7 $120.34   11.520%   $134.2032   $134.20   $134.20   $134.20  
  7 purchase totals = $804.84       $878.3137   $878.30   $878.35   $878.40