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 $107.85   10.634%   $119.3188   $119.32   $119.30   $119.30  
  Purchase #2 $177.40   13.741%   $201.7765   $201.78   $201.80   $201.80  
  Purchase #3 $181.28   8.116%   $195.9927   $195.99   $196.00   $196.00  
  Purchase #4 $59.27   8.418%   $64.2593   $64.26   $64.25   $64.30  
  Purchase #5 $82.87   12.407%   $93.1517   $93.15   $93.15   $93.20  
  Purchase #6 $229.49   6.709%   $244.8865   $244.89   $244.90   $244.90  
  Purchase #7 $42.58   9.849%   $46.7737   $46.77   $46.75   $46.80  
  7 purchase totals = $880.74       $966.1592   $966.16   $966.15   $966.30