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 $227.47   3.194%   $234.7354   $234.74   $234.75   $234.70  
  Purchase #2 $123.38   8.243%   $133.5502   $133.55   $133.55   $133.60  
  Purchase #3 $53.50   12.326%   $60.0944   $60.09   $60.10   $60.10  
  Purchase #4 $96.33   7.173%   $103.2398   $103.24   $103.25   $103.20  
  Purchase #5 $101.89   12.797%   $114.9289   $114.93   $114.95   $114.90  
  Purchase #6 $53.26   12.694%   $60.0208   $60.02   $60.00   $60.00  
  Purchase #7 $107.72   11.764%   $120.3922   $120.39   $120.40   $120.40  
  7 purchase totals = $763.55       $826.9617   $826.96   $827.00   $826.90