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 $203.28   5.589%   $214.6413   $214.64   $214.65   $214.60  
  Purchase #2 $79.55   11.285%   $88.5272   $88.53   $88.55   $88.50  
  Purchase #3 $186.82   13.604%   $212.235   $212.24   $212.25   $212.20  
  Purchase #4 $89.37   5.813%   $94.5651   $94.57   $94.55   $94.60  
  Purchase #5 $72.73   5.542%   $76.7607   $76.76   $76.75   $76.80  
  Purchase #6 $182.34   7.323%   $195.6928   $195.69   $195.70   $195.70  
  Purchase #7 $108.32   4.480%   $113.1727   $113.17   $113.15   $113.20  
  7 purchase totals = $922.41       $995.5948   $995.60   $995.60   $995.60