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 $207.86   10.829%   $230.3692   $230.37   $230.35   $230.40  
  Purchase #2 $244.55   6.156%   $259.6045   $259.60   $259.60   $259.60  
  Purchase #3 $240.68   3.342%   $248.7235   $248.72   $248.70   $248.70  
  Purchase #4 $27.76   8.764%   $30.1929   $30.19   $30.20   $30.20  
  Purchase #5 $167.80   6.367%   $178.4838   $178.48   $178.50   $178.50  
  Purchase #6 $127.89   10.158%   $140.8811   $140.88   $140.90   $140.90  
  Purchase #7 $196.53   10.609%   $217.3799   $217.38   $217.40   $217.40  
  7 purchase totals = $1,213.07       $1,305.6349   $1,305.62   $1,305.65   $1,305.70