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 $77.65   6.477%   $82.6794   $82.68   $82.70   $82.70  
  Purchase #2 $211.81   6.177%   $224.8935   $224.89   $224.90   $224.90  
  Purchase #3 $178.86   5.257%   $188.2627   $188.26   $188.25   $188.30  
  Purchase #4 $130.49   13.234%   $147.759   $147.76   $147.75   $147.80  
  Purchase #5 $180.56   5.489%   $190.4709   $190.47   $190.45   $190.50  
  Purchase #6 $7.83   9.217%   $8.5517   $8.55   $8.55   $8.60  
  Purchase #7 $106.78   11.453%   $119.0095   $119.01   $119.00   $119.00  
  7 purchase totals = $893.98       $961.6267   $961.62   $961.60   $961.80