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 $182.48   7.725%   $196.5766   $196.58   $196.60   $196.60  
  Purchase #2 $145.91   3.724%   $151.3437   $151.34   $151.35   $151.30  
  Purchase #3 $28.70   13.636%   $32.6135   $32.61   $32.60   $32.60  
  Purchase #4 $164.53   7.839%   $177.4275   $177.43   $177.45   $177.40  
  Purchase #5 $58.98   8.346%   $63.9025   $63.90   $63.90   $63.90  
  Purchase #6 $69.52   6.216%   $73.8414   $73.84   $73.85   $73.80  
  Purchase #7 $114.97   9.154%   $125.4944   $125.49   $125.50   $125.50  
  7 purchase totals = $765.09       $821.1996   $821.19   $821.25   $821.10