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 $141.41   3.357%   $146.1571   $146.16   $146.15   $146.20  
  Purchase #2 $241.56   11.119%   $268.4191   $268.42   $268.40   $268.40  
  Purchase #3 $46.32   12.769%   $52.2346   $52.23   $52.25   $52.20  
  Purchase #4 $23.55   3.312%   $24.33   $24.33   $24.35   $24.30  
  Purchase #5 $195.81   3.522%   $202.7064   $202.71   $202.70   $202.70  
  Purchase #6 $127.65   8.588%   $138.6126   $138.61   $138.60   $138.60  
  Purchase #7 $192.65   4.346%   $201.0226   $201.02   $201.00   $201.00  
  7 purchase totals = $968.95       $1,033.4824   $1,033.48   $1,033.45   $1,033.40