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 $210.65   13.709%   $239.528   $239.53   $239.55   $239.50  
  Purchase #2 $119.68   4.616%   $125.2044   $125.20   $125.20   $125.20  
  Purchase #3 $184.72   4.365%   $192.783   $192.78   $192.80   $192.80  
  Purchase #4 $156.80   9.541%   $171.7603   $171.76   $171.75   $171.80  
  Purchase #5 $113.99   10.205%   $125.6227   $125.62   $125.60   $125.60  
  Purchase #6 $179.80   3.557%   $186.1955   $186.20   $186.20   $186.20  
  Purchase #7 $63.59   7.256%   $68.2041   $68.20   $68.20   $68.20  
  7 purchase totals = $1,029.23       $1,109.2980   $1,109.29   $1,109.30   $1,109.30