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 $61.53   10.543%   $68.0171   $68.02   $68.00   $68.00  
  Purchase #2 $174.76   12.626%   $196.8252   $196.83   $196.85   $196.80  
  Purchase #3 $58.26   4.222%   $60.7197   $60.72   $60.70   $60.70  
  Purchase #4 $188.99   10.463%   $208.764   $208.76   $208.75   $208.80  
  Purchase #5 $21.35   11.308%   $23.7643   $23.76   $23.75   $23.80  
  Purchase #6 $233.69   3.661%   $242.2454   $242.25   $242.25   $242.20  
  Purchase #7 $142.84   7.412%   $153.4273   $153.43   $153.45   $153.40  
  7 purchase totals = $881.42       $953.7630   $953.77   $953.75   $953.70