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 $235.68   10.522%   $260.4782   $260.48   $260.50   $260.50  
  Purchase #2 $122.29   7.856%   $131.8971   $131.90   $131.90   $131.90  
  Purchase #3 $167.71   3.515%   $173.605   $173.61   $173.60   $173.60  
  Purchase #4 $12.99   7.832%   $14.0074   $14.01   $14.00   $14.00  
  Purchase #5 $228.58   5.592%   $241.3622   $241.36   $241.35   $241.40  
  Purchase #6 $141.76   7.855%   $152.8952   $152.90   $152.90   $152.90  
  Purchase #7 $174.53   13.518%   $198.123   $198.12   $198.10   $198.10  
  7 purchase totals = $1,083.54       $1,172.3681   $1,172.38   $1,172.35   $1,172.40