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 $55.90   7.365%   $60.017   $60.02   $60.00   $60.00  
  Purchase #2 $217.34   10.330%   $239.7912   $239.79   $239.80   $239.80  
  Purchase #3 $7.43   8.151%   $8.0356   $8.04   $8.05   $8.00  
  Purchase #4 $143.38   6.566%   $152.7943   $152.79   $152.80   $152.80  
  Purchase #5 $113.53   7.863%   $122.4569   $122.46   $122.45   $122.50  
  Purchase #6 $175.64   12.127%   $196.9399   $196.94   $196.95   $196.90  
  Purchase #7 $43.60   7.674%   $46.9459   $46.95   $46.95   $46.90  
  7 purchase totals = $756.82       $826.9808   $826.99   $827.00   $826.90