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 $59.82   4.451%   $62.4826   $62.48   $62.50   $62.50  
  Purchase #2 $232.94   6.773%   $248.717   $248.72   $248.70   $248.70  
  Purchase #3 $30.86   6.652%   $32.9128   $32.91   $32.90   $32.90  
  Purchase #4 $156.31   5.412%   $164.7695   $164.77   $164.75   $164.80  
  Purchase #5 $239.65   3.507%   $248.0545   $248.05   $248.05   $248.10  
  Purchase #6 $48.78   5.229%   $51.3307   $51.33   $51.35   $51.30  
  Purchase #7 $27.58   9.162%   $30.1069   $30.11   $30.10   $30.10  
  7 purchase totals = $795.94       $838.3740   $838.37   $838.35   $838.40