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 $67.67   12.188%   $75.9176   $75.92   $75.90   $75.90  
  Purchase #2 $32.51   10.586%   $35.9515   $35.95   $35.95   $36.00  
  Purchase #3 $147.63   5.696%   $156.039   $156.04   $156.05   $156.00  
  Purchase #4 $189.99   9.869%   $208.7401   $208.74   $208.75   $208.70  
  Purchase #5 $67.54   11.761%   $75.4834   $75.48   $75.50   $75.50  
  Purchase #6 $236.49   9.383%   $258.6799   $258.68   $258.70   $258.70  
  Purchase #7 $43.53   11.539%   $48.5529   $48.55   $48.55   $48.60  
  7 purchase totals = $785.36       $859.3644   $859.36   $859.40   $859.40