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 $55.26   13.249%   $62.5814   $62.58   $62.60   $62.60  
  Purchase #2 $159.83   8.134%   $172.8306   $172.83   $172.85   $172.80  
  Purchase #3 $152.31   5.303%   $160.387   $160.39   $160.40   $160.40  
  Purchase #4 $14.48   11.259%   $16.1103   $16.11   $16.10   $16.10  
  Purchase #5 $214.37   5.553%   $226.274   $226.27   $226.25   $226.30  
  Purchase #6 $15.44   6.751%   $16.4824   $16.48   $16.50   $16.50  
  Purchase #7 $228.95   7.510%   $246.1441   $246.14   $246.15   $246.10  
  7 purchase totals = $840.64       $900.8098   $900.80   $900.85   $900.80