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 $90.88   3.682%   $94.2262   $94.23   $94.25   $94.20  
  Purchase #2 $60.41   5.801%   $63.9144   $63.91   $63.90   $63.90  
  Purchase #3 $66.90   8.467%   $72.5644   $72.56   $72.55   $72.60  
  Purchase #4 $201.73   3.312%   $208.4113   $208.41   $208.40   $208.40  
  Purchase #5 $41.95   12.274%   $47.0989   $47.10   $47.10   $47.10  
  Purchase #6 $50.92   3.590%   $52.748   $52.75   $52.75   $52.70  
  Purchase #7 $64.78   7.245%   $69.4733   $69.47   $69.45   $69.50  
  7 purchase totals = $577.57       $608.4365   $608.43   $608.40   $608.40