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 $69.66   11.706%   $77.8144   $77.81   $77.80   $77.80  
  Purchase #2 $64.86   4.495%   $67.7755   $67.78   $67.80   $67.80  
  Purchase #3 $156.66   11.796%   $175.1396   $175.14   $175.15   $175.10  
  Purchase #4 $161.59   12.738%   $182.1733   $182.17   $182.15   $182.20  
  Purchase #5 $57.72   5.493%   $60.8906   $60.89   $60.90   $60.90  
  Purchase #6 $171.93   13.447%   $195.0494   $195.05   $195.05   $195.00  
  Purchase #7 $184.39   4.457%   $192.6083   $192.61   $192.60   $192.60  
  7 purchase totals = $866.81       $951.4511   $951.45   $951.45   $951.40