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 $219.96   7.114%   $235.608   $235.61   $235.60   $235.60  
  Purchase #2 $225.70   11.685%   $252.073   $252.07   $252.05   $252.10  
  Purchase #3 $34.96   5.859%   $37.0083   $37.01   $37.00   $37.00  
  Purchase #4 $33.61   4.756%   $35.2085   $35.21   $35.20   $35.20  
  Purchase #5 $94.44   3.190%   $97.4526   $97.45   $97.45   $97.50  
  Purchase #6 $60.65   12.689%   $68.3459   $68.35   $68.35   $68.30  
  Purchase #7 $103.40   10.798%   $114.5651   $114.57   $114.55   $114.60  
  7 purchase totals = $772.72       $840.2614   $840.27   $840.20   $840.30