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 $223.34   5.738%   $236.1552   $236.16   $236.15   $236.20  
  Purchase #2 $248.46   4.197%   $258.8879   $258.89   $258.90   $258.90  
  Purchase #3 $16.42   7.721%   $17.6878   $17.69   $17.70   $17.70  
  Purchase #4 $208.61   3.809%   $216.556   $216.56   $216.55   $216.60  
  Purchase #5 $48.81   13.498%   $55.3984   $55.40   $55.40   $55.40  
  Purchase #6 $140.82   9.855%   $154.6978   $154.70   $154.70   $154.70  
  Purchase #7 $83.77   10.807%   $92.823   $92.82   $92.80   $92.80  
  7 purchase totals = $970.23       $1,032.2061   $1,032.22   $1,032.20   $1,032.30