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 $196.35   3.608%   $203.4343   $203.43   $203.45   $203.40  
  Purchase #2 $192.31   8.436%   $208.5333   $208.53   $208.55   $208.50  
  Purchase #3 $45.25   9.183%   $49.4053   $49.41   $49.40   $49.40  
  Purchase #4 $82.94   4.602%   $86.7569   $86.76   $86.75   $86.80  
  Purchase #5 $231.57   13.184%   $262.1002   $262.10   $262.10   $262.10  
  Purchase #6 $86.80   6.453%   $92.4012   $92.40   $92.40   $92.40  
  Purchase #7 $118.81   7.133%   $127.2847   $127.28   $127.30   $127.30  
  7 purchase totals = $954.03       $1,029.9159   $1,029.91   $1,029.95   $1,029.90