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 $33.70   3.296%   $34.8108   $34.81   $34.80   $34.80  
  Purchase #2 $240.92   10.535%   $266.3009   $266.30   $266.30   $266.30  
  Purchase #3 $62.69   11.800%   $70.0874   $70.09   $70.10   $70.10  
  Purchase #4 $34.87   11.401%   $38.8455   $38.85   $38.85   $38.80  
  Purchase #5 $67.30   5.831%   $71.2243   $71.22   $71.20   $71.20  
  Purchase #6 $225.82   5.242%   $237.6575   $237.66   $237.65   $237.70  
  Purchase #7 $230.39   4.432%   $240.6009   $240.60   $240.60   $240.60  
  7 purchase totals = $895.69       $959.5273   $959.53   $959.50   $959.50