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 $244.70   3.237%   $252.6209   $252.62   $252.60   $252.60  
  Purchase #2 $185.40   4.473%   $193.6929   $193.69   $193.70   $193.70  
  Purchase #3 $141.94   9.460%   $155.3675   $155.37   $155.35   $155.40  
  Purchase #4 $240.76   3.274%   $248.6425   $248.64   $248.65   $248.60  
  Purchase #5 $186.44   6.300%   $198.1857   $198.19   $198.20   $198.20  
  Purchase #6 $120.58   12.128%   $135.2039   $135.20   $135.20   $135.20  
  Purchase #7 $68.48   7.802%   $73.8228   $73.82   $73.80   $73.80  
  7 purchase totals = $1,188.30       $1,257.5362   $1,257.53   $1,257.50   $1,257.50