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 $169.96   9.848%   $186.6977   $186.70   $186.70   $186.70  
  Purchase #2 $139.93   8.154%   $151.3399   $151.34   $151.35   $151.30  
  Purchase #3 $236.88   4.365%   $247.2198   $247.22   $247.20   $247.20  
  Purchase #4 $165.31   8.395%   $179.1878   $179.19   $179.20   $179.20  
  Purchase #5 $116.49   9.333%   $127.362   $127.36   $127.35   $127.40  
  Purchase #6 $164.37   13.104%   $185.909   $185.91   $185.90   $185.90  
  Purchase #7 $215.36   5.542%   $227.2953   $227.30   $227.30   $227.30  
  7 purchase totals = $1,208.30       $1,305.0115   $1,305.02   $1,305.00   $1,305.00