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 $228.88   8.322%   $247.9274   $247.93   $247.95   $247.90  
  Purchase #2 $19.87   7.550%   $21.3702   $21.37   $21.35   $21.40  
  Purchase #3 $114.40   13.133%   $129.4242   $129.42   $129.40   $129.40  
  Purchase #4 $156.54   5.153%   $164.6065   $164.61   $164.60   $164.60  
  Purchase #5 $142.80   6.441%   $151.9977   $152.00   $152.00   $152.00  
  Purchase #6 $77.38   7.783%   $83.4025   $83.40   $83.40   $83.40  
  Purchase #7 $230.76   3.383%   $238.5666   $238.57   $238.55   $238.60  
  7 purchase totals = $970.63       $1,037.2951   $1,037.30   $1,037.25   $1,037.30