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 $85.25   13.238%   $96.5354   $96.54   $96.55   $96.50  
  Purchase #2 $34.69   11.718%   $38.755   $38.76   $38.75   $38.80  
  Purchase #3 $226.33   9.614%   $248.0894   $248.09   $248.10   $248.10  
  Purchase #4 $70.69   12.344%   $79.416   $79.42   $79.40   $79.40  
  Purchase #5 $38.35   11.833%   $42.888   $42.89   $42.90   $42.90  
  Purchase #6 $217.35   7.129%   $232.8449   $232.84   $232.85   $232.80  
  Purchase #7 $17.83   4.863%   $18.6971   $18.70   $18.70   $18.70  
  7 purchase totals = $690.49       $757.2258   $757.24   $757.25   $757.20