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 $184.86   12.314%   $207.6237   $207.62   $207.60   $207.60  
  Purchase #2 $139.66   4.370%   $145.7631   $145.76   $145.75   $145.80  
  Purchase #3 $125.77   6.619%   $134.0947   $134.09   $134.10   $134.10  
  Purchase #4 $88.93   8.626%   $96.6011   $96.60   $96.60   $96.60  
  Purchase #5 $69.25   6.713%   $73.8988   $73.90   $73.90   $73.90  
  Purchase #6 $159.29   3.788%   $165.3239   $165.32   $165.30   $165.30  
  Purchase #7 $67.76   7.661%   $72.9511   $72.95   $72.95   $73.00  
  7 purchase totals = $835.52       $896.2564   $896.24   $896.20   $896.30