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 $235.53   11.247%   $262.0201   $262.02   $262.00   $262.00  
  Purchase #2 $123.63   12.143%   $138.6424   $138.64   $138.65   $138.60  
  Purchase #3 $176.88   10.273%   $195.0509   $195.05   $195.05   $195.10  
  Purchase #4 $211.97   3.768%   $219.957   $219.96   $219.95   $220.00  
  Purchase #5 $68.47   5.242%   $72.0592   $72.06   $72.05   $72.10  
  Purchase #6 $60.82   5.177%   $63.9687   $63.97   $63.95   $64.00  
  Purchase #7 $169.47   10.660%   $187.5355   $187.54   $187.55   $187.50  
  7 purchase totals = $1,046.77       $1,139.2338   $1,139.24   $1,139.20   $1,139.30