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 $60.95   8.198%   $65.9467   $65.95   $65.95   $65.90  
  Purchase #2 $116.43   4.124%   $121.2316   $121.23   $121.25   $121.20  
  Purchase #3 $36.80   4.654%   $38.5127   $38.51   $38.50   $38.50  
  Purchase #4 $111.85   7.798%   $120.5721   $120.57   $120.55   $120.60  
  Purchase #5 $115.51   3.576%   $119.6406   $119.64   $119.65   $119.60  
  Purchase #6 $110.76   13.848%   $126.098   $126.10   $126.10   $126.10  
  Purchase #7 $85.41   4.696%   $89.4209   $89.42   $89.40   $89.40  
  7 purchase totals = $637.71       $681.4226   $681.42   $681.40   $681.30