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 $212.71   11.614%   $237.4141   $237.41   $237.40   $237.40  
  Purchase #2 $14.73   10.193%   $16.2314   $16.23   $16.25   $16.20  
  Purchase #3 $64.57   6.824%   $68.9763   $68.98   $69.00   $69.00  
  Purchase #4 $29.25   3.818%   $30.3668   $30.37   $30.35   $30.40  
  Purchase #5 $105.54   9.499%   $115.5652   $115.57   $115.55   $115.60  
  Purchase #6 $193.45   4.267%   $201.7045   $201.70   $201.70   $201.70  
  Purchase #7 $226.38   9.579%   $248.0649   $248.06   $248.05   $248.10  
  7 purchase totals = $846.63       $918.3232   $918.32   $918.30   $918.40