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 $239.45   12.398%   $269.137   $269.14   $269.15   $269.10  
  Purchase #2 $79.67   6.724%   $85.027   $85.03   $85.05   $85.00  
  Purchase #3 $208.64   6.105%   $221.3775   $221.38   $221.40   $221.40  
  Purchase #4 $35.85   8.862%   $39.027   $39.03   $39.05   $39.00  
  Purchase #5 $246.30   9.598%   $269.9399   $269.94   $269.95   $269.90  
  Purchase #6 $8.92   10.571%   $9.8629   $9.86   $9.85   $9.90  
  Purchase #7 $109.31   13.254%   $123.7979   $123.80   $123.80   $123.80  
  7 purchase totals = $928.14       $1,018.1692   $1,018.18   $1,018.25   $1,018.10