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 $72.42   10.791%   $80.2348   $80.23   $80.25   $80.20  
  Purchase #2 $247.99   8.163%   $268.2334   $268.23   $268.25   $268.20  
  Purchase #3 $58.85   8.215%   $63.6845   $63.68   $63.70   $63.70  
  Purchase #4 $102.75   11.258%   $114.3176   $114.32   $114.30   $114.30  
  Purchase #5 $246.94   11.295%   $274.8319   $274.83   $274.85   $274.80  
  Purchase #6 $108.52   9.284%   $118.595   $118.60   $118.60   $118.60  
  Purchase #7 $12.50   12.495%   $14.0619   $14.06   $14.05   $14.10  
  7 purchase totals = $849.97       $933.9591   $933.95   $934.00   $933.90