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 $64.96   13.321%   $73.6133   $73.61   $73.60   $73.60  
  Purchase #2 $211.31   11.712%   $236.0586   $236.06   $236.05   $236.10  
  Purchase #3 $85.71   5.829%   $90.706   $90.71   $90.70   $90.70  
  Purchase #4 $182.94   5.526%   $193.0493   $193.05   $193.05   $193.00  
  Purchase #5 $165.98   7.465%   $178.3704   $178.37   $178.35   $178.40  
  Purchase #6 $116.58   13.577%   $132.4081   $132.41   $132.40   $132.40  
  Purchase #7 $250.56   5.792%   $265.0724   $265.07   $265.05   $265.10  
  7 purchase totals = $1,078.04       $1,169.2781   $1,169.28   $1,169.20   $1,169.30