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 $213.58   13.185%   $241.7405   $241.74   $241.75   $241.70  
  Purchase #2 $152.86   8.232%   $165.4434   $165.44   $165.45   $165.40  
  Purchase #3 $117.49   3.596%   $121.7149   $121.71   $121.70   $121.70  
  Purchase #4 $230.80   10.246%   $254.4478   $254.45   $254.45   $254.40  
  Purchase #5 $130.80   6.758%   $139.6395   $139.64   $139.65   $139.60  
  Purchase #6 $102.26   9.407%   $111.8796   $111.88   $111.90   $111.90  
  Purchase #7 $233.40   13.643%   $265.2428   $265.24   $265.25   $265.20  
  7 purchase totals = $1,181.19       $1,300.1085   $1,300.10   $1,300.15   $1,299.90