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 $239.55   10.473%   $264.6381   $264.64   $264.65   $264.60  
  Purchase #2 $238.41   4.244%   $248.5281   $248.53   $248.55   $248.50  
  Purchase #3 $156.31   5.282%   $164.5663   $164.57   $164.55   $164.60  
  Purchase #4 $150.61   11.460%   $167.8699   $167.87   $167.85   $167.90  
  Purchase #5 $11.64   5.325%   $12.2598   $12.26   $12.25   $12.30  
  Purchase #6 $213.57   10.578%   $236.1614   $236.16   $236.15   $236.20  
  Purchase #7 $141.47   7.794%   $152.4962   $152.50   $152.50   $152.50  
  7 purchase totals = $1,151.56       $1,246.5198   $1,246.53   $1,246.50   $1,246.60