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 $146.25   10.744%   $161.9631   $161.96   $161.95   $162.00  
  Purchase #2 $213.56   10.827%   $236.6821   $236.68   $236.70   $236.70  
  Purchase #3 $15.55   9.148%   $16.9725   $16.97   $16.95   $17.00  
  Purchase #4 $72.49   12.721%   $81.7115   $81.71   $81.70   $81.70  
  Purchase #5 $230.85   13.436%   $261.867   $261.87   $261.85   $261.90  
  Purchase #6 $165.27   6.483%   $175.9845   $175.98   $176.00   $176.00  
  Purchase #7 $233.52   6.332%   $248.3065   $248.31   $248.30   $248.30  
  7 purchase totals = $1,077.49       $1,183.4872   $1,183.48   $1,183.45   $1,183.60