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 $24.46   8.597%   $26.5628   $26.56   $26.55   $26.60  
  Purchase #2 $195.61   6.715%   $208.7452   $208.75   $208.75   $208.70  
  Purchase #3 $10.94   9.469%   $11.9759   $11.98   $12.00   $12.00  
  Purchase #4 $82.76   13.621%   $94.0327   $94.03   $94.05   $94.00  
  Purchase #5 $34.61   6.745%   $36.9444   $36.94   $36.95   $36.90  
  Purchase #6 $79.51   12.462%   $89.4185   $89.42   $89.40   $89.40  
  Purchase #7 $140.28   9.362%   $153.413   $153.41   $153.40   $153.40  
  7 purchase totals = $568.17       $621.0925   $621.09   $621.10   $621.00