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 $58.93   4.497%   $61.5801   $61.58   $61.60   $61.60  
  Purchase #2 $215.44   5.296%   $226.8497   $226.85   $226.85   $226.80  
  Purchase #3 $190.58   5.308%   $200.696   $200.70   $200.70   $200.70  
  Purchase #4 $38.94   12.801%   $43.9247   $43.92   $43.90   $43.90  
  Purchase #5 $128.85   5.302%   $135.6816   $135.68   $135.70   $135.70  
  Purchase #6 $75.98   11.156%   $84.4563   $84.46   $84.45   $84.50  
  Purchase #7 $186.45   10.873%   $206.7227   $206.72   $206.70   $206.70  
  7 purchase totals = $895.17       $959.9111   $959.91   $959.90   $959.90