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 $237.43   4.471%   $248.0455   $248.05   $248.05   $248.00  
  Purchase #2 $178.76   7.799%   $192.7015   $192.70   $192.70   $192.70  
  Purchase #3 $72.46   5.769%   $76.6402   $76.64   $76.65   $76.60  
  Purchase #4 $127.60   13.747%   $145.1412   $145.14   $145.15   $145.10  
  Purchase #5 $174.94   13.356%   $198.305   $198.31   $198.30   $198.30  
  Purchase #6 $239.91   6.759%   $256.1255   $256.13   $256.15   $256.10  
  Purchase #7 $119.36   9.836%   $131.1002   $131.10   $131.10   $131.10  
  7 purchase totals = $1,150.46       $1,248.0591   $1,248.07   $1,248.10   $1,247.90