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 $223.84   8.240%   $242.2844   $242.28   $242.30   $242.30  
  Purchase #2 $196.76   13.184%   $222.7008   $222.70   $222.70   $222.70  
  Purchase #3 $178.40   9.283%   $194.9609   $194.96   $194.95   $195.00  
  Purchase #4 $165.45   3.626%   $171.4492   $171.45   $171.45   $171.40  
  Purchase #5 $44.92   12.320%   $50.4541   $50.45   $50.45   $50.50  
  Purchase #6 $103.63   10.563%   $114.5764   $114.58   $114.60   $114.60  
  Purchase #7 $13.68   9.253%   $14.9458   $14.95   $14.95   $14.90  
  7 purchase totals = $926.68       $1,011.3716   $1,011.37   $1,011.40   $1,011.40