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 $57.37   13.381%   $65.0467   $65.05   $65.05   $65.00  
  Purchase #2 $209.95   12.542%   $236.2819   $236.28   $236.30   $236.30  
  Purchase #3 $184.73   7.626%   $198.8175   $198.82   $198.80   $198.80  
  Purchase #4 $82.98   9.337%   $90.7278   $90.73   $90.75   $90.70  
  Purchase #5 $245.94   5.162%   $258.6354   $258.64   $258.65   $258.60  
  Purchase #6 $15.43   9.557%   $16.9046   $16.90   $16.90   $16.90  
  Purchase #7 $177.77   7.551%   $191.1934   $191.19   $191.20   $191.20  
  7 purchase totals = $974.17       $1,057.6073   $1,057.61   $1,057.65   $1,057.50