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 $151.95   3.291%   $156.9507   $156.95   $156.95   $157.00  
  Purchase #2 $240.38   12.304%   $269.9564   $269.96   $269.95   $270.00  
  Purchase #3 $14.95   3.724%   $15.5067   $15.51   $15.50   $15.50  
  Purchase #4 $208.44   11.133%   $231.6456   $231.65   $231.65   $231.60  
  Purchase #5 $163.61   3.308%   $169.0222   $169.02   $169.00   $169.00  
  Purchase #6 $96.56   13.538%   $109.6323   $109.63   $109.65   $109.60  
  Purchase #7 $62.67   8.730%   $68.1411   $68.14   $68.15   $68.10  
  7 purchase totals = $938.56       $1,020.8550   $1,020.86   $1,020.85   $1,020.80