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 $29.93   8.688%   $32.5303   $32.53   $32.55   $32.50  
  Purchase #2 $46.37   7.190%   $49.704   $49.70   $49.70   $49.70  
  Purchase #3 $38.83   11.814%   $43.4174   $43.42   $43.40   $43.40  
  Purchase #4 $105.51   8.779%   $114.7727   $114.77   $114.75   $114.80  
  Purchase #5 $34.65   6.571%   $36.9269   $36.93   $36.95   $36.90  
  Purchase #6 $210.77   13.182%   $238.5537   $238.55   $238.55   $238.60  
  Purchase #7 $192.85   9.245%   $210.679   $210.68   $210.70   $210.70  
  7 purchase totals = $658.91       $726.5840   $726.58   $726.60   $726.60