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 $88.55   4.353%   $92.4046   $92.40   $92.40   $92.40  
  Purchase #2 $186.79   13.260%   $211.5584   $211.56   $211.55   $211.60  
  Purchase #3 $23.55   12.535%   $26.502   $26.50   $26.50   $26.50  
  Purchase #4 $134.59   6.111%   $142.8148   $142.81   $142.80   $142.80  
  Purchase #5 $6.32   6.447%   $6.7275   $6.73   $6.75   $6.70  
  Purchase #6 $65.35   10.632%   $72.298   $72.30   $72.30   $72.30  
  Purchase #7 $240.90   4.696%   $252.2127   $252.21   $252.20   $252.20  
  7 purchase totals = $746.05       $804.5180   $804.51   $804.50   $804.50