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 $133.80   13.451%   $151.7974   $151.80   $151.80   $151.80  
  Purchase #2 $66.97   8.527%   $72.6805   $72.68   $72.70   $72.70  
  Purchase #3 $147.99   4.216%   $154.2293   $154.23   $154.25   $154.20  
  Purchase #4 $116.32   9.721%   $127.6275   $127.63   $127.65   $127.60  
  Purchase #5 $34.69   10.828%   $38.4462   $38.45   $38.45   $38.40  
  Purchase #6 $214.70   9.209%   $234.4717   $234.47   $234.45   $234.50  
  Purchase #7 $218.70   10.797%   $242.313   $242.31   $242.30   $242.30  
  7 purchase totals = $933.17       $1,021.5656   $1,021.57   $1,021.60   $1,021.50