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 $244.78   3.724%   $253.8956   $253.90   $253.90   $253.90  
  Purchase #2 $206.50   3.269%   $213.2505   $213.25   $213.25   $213.30  
  Purchase #3 $63.90   6.830%   $68.2644   $68.26   $68.25   $68.30  
  Purchase #4 $34.66   6.656%   $36.967   $36.97   $36.95   $37.00  
  Purchase #5 $60.26   8.304%   $65.264   $65.26   $65.25   $65.30  
  Purchase #6 $16.92   9.438%   $18.5169   $18.52   $18.50   $18.50  
  Purchase #7 $248.38   11.758%   $277.5845   $277.58   $277.60   $277.60  
  7 purchase totals = $875.40       $933.7429   $933.74   $933.70   $933.90