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 $164.53   6.148%   $174.6453   $174.65   $174.65   $174.60  
  Purchase #2 $221.99   4.265%   $231.4579   $231.46   $231.45   $231.50  
  Purchase #3 $68.32   8.293%   $73.9858   $73.99   $74.00   $74.00  
  Purchase #4 $70.49   8.752%   $76.6593   $76.66   $76.65   $76.70  
  Purchase #5 $175.89   13.806%   $200.1734   $200.17   $200.15   $200.20  
  Purchase #6 $130.78   9.305%   $142.9491   $142.95   $142.95   $142.90  
  Purchase #7 $156.52   12.853%   $176.6375   $176.64   $176.65   $176.60  
  7 purchase totals = $988.52       $1,076.5083   $1,076.52   $1,076.50   $1,076.50